Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $231.82   5.510%   $244.5933   $244.59   $244.60   $244.60  
  Purchase #2 $246.74   6.809%   $263.5405   $263.54   $263.55   $263.50  
  Purchase #3 $247.96   4.844%   $259.9712   $259.97   $259.95   $260.00  
  Purchase #4 $14.64   5.122%   $15.3899   $15.39   $15.40   $15.40  
  Purchase #5 $243.42   9.591%   $266.7664   $266.77   $266.75   $266.80  
  Purchase #6 $176.89   11.537%   $197.2978   $197.30   $197.30   $197.30  
  Purchase #7 $161.44   5.686%   $170.6195   $170.62   $170.60   $170.60  
  7 purchase totals = $1,322.91       $1,418.1786   $1,418.18   $1,418.15   $1,418.20