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 $221.60   11.417%   $246.9001   $246.90   $246.90   $246.90  
  Purchase #2 $153.96   8.294%   $166.7294   $166.73   $166.75   $166.70  
  Purchase #3 $21.35   5.299%   $22.4813   $22.48   $22.50   $22.50  
  Purchase #4 $210.50   11.216%   $234.1097   $234.11   $234.10   $234.10  
  Purchase #5 $58.69   8.303%   $63.563   $63.56   $63.55   $63.60  
  Purchase #6 $125.98   4.864%   $132.1077   $132.11   $132.10   $132.10  
  Purchase #7 $190.84   8.727%   $207.4946   $207.49   $207.50   $207.50  
  7 purchase totals = $982.92       $1,073.3858   $1,073.38   $1,073.40   $1,073.40