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 $58.98   8.412%   $63.9414   $63.94   $63.95   $63.90  
  Purchase #2 $145.71   10.856%   $161.5283   $161.53   $161.55   $161.50  
  Purchase #3 $145.76   9.259%   $159.2559   $159.26   $159.25   $159.30  
  Purchase #4 $248.71   13.496%   $282.2759   $282.28   $282.30   $282.30  
  Purchase #5 $211.27   13.343%   $239.4598   $239.46   $239.45   $239.50  
  Purchase #6 $242.54   8.654%   $263.5294   $263.53   $263.55   $263.50  
  Purchase #7 $243.60   3.498%   $252.1211   $252.12   $252.10   $252.10  
  7 purchase totals = $1,296.57       $1,422.1118   $1,422.12   $1,422.15   $1,422.10