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 $57.66   12.298%   $64.751   $64.75   $64.75   $64.80  
  Purchase #2 $67.68   13.120%   $76.5596   $76.56   $76.55   $76.60  
  Purchase #3 $62.43   8.320%   $67.6242   $67.62   $67.60   $67.60  
  Purchase #4 $237.93   11.269%   $264.7423   $264.74   $264.75   $264.70  
  Purchase #5 $148.68   5.382%   $156.682   $156.68   $156.70   $156.70  
  Purchase #6 $108.65   9.640%   $119.1239   $119.12   $119.10   $119.10  
  Purchase #7 $195.39   10.327%   $215.5679   $215.57   $215.55   $215.60  
  7 purchase totals = $878.42       $965.0509   $965.04   $965.00   $965.10