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 $73.71   3.228%   $76.0894   $76.09   $76.10   $76.10  
  Purchase #2 $53.43   6.616%   $56.9649   $56.96   $56.95   $57.00  
  Purchase #3 $250.80   4.776%   $262.7782   $262.78   $262.80   $262.80  
  Purchase #4 $193.82   11.351%   $215.8205   $215.82   $215.80   $215.80  
  Purchase #5 $164.50   5.426%   $173.4258   $173.43   $173.45   $173.40  
  Purchase #6 $211.68   10.702%   $234.334   $234.33   $234.35   $234.30  
  Purchase #7 $132.93   11.558%   $148.294   $148.29   $148.30   $148.30  
  7 purchase totals = $1,080.87       $1,167.7068   $1,167.70   $1,167.75   $1,167.70