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 $130.55   8.459%   $141.5932   $141.59   $141.60   $141.60  
  Purchase #2 $241.58   10.104%   $265.9892   $265.99   $266.00   $266.00  
  Purchase #3 $202.82   11.599%   $226.3451   $226.35   $226.35   $226.30  
  Purchase #4 $91.84   10.773%   $101.7339   $101.73   $101.75   $101.70  
  Purchase #5 $24.29   3.220%   $25.0721   $25.07   $25.05   $25.10  
  Purchase #6 $27.73   6.185%   $29.4451   $29.45   $29.45   $29.40  
  Purchase #7 $125.84   5.761%   $133.0896   $133.09   $133.10   $133.10  
  7 purchase totals = $844.65       $923.2682   $923.27   $923.30   $923.20