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 $125.67   12.805%   $141.762   $141.76   $141.75   $141.80  
  Purchase #2 $73.62   3.751%   $76.3815   $76.38   $76.40   $76.40  
  Purchase #3 $162.88   4.752%   $170.6201   $170.62   $170.60   $170.60  
  Purchase #4 $107.31   12.285%   $120.493   $120.49   $120.50   $120.50  
  Purchase #5 $21.84   10.767%   $24.1915   $24.19   $24.20   $24.20  
  Purchase #6 $205.80   10.667%   $227.7527   $227.75   $227.75   $227.80  
  Purchase #7 $58.94   5.818%   $62.3691   $62.37   $62.35   $62.40  
  7 purchase totals = $756.06       $823.5699   $823.56   $823.55   $823.70