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 $224.96   8.744%   $244.6305   $244.63   $244.65   $244.60  
  Purchase #2 $201.74   11.681%   $225.3052   $225.31   $225.30   $225.30  
  Purchase #3 $125.68   3.856%   $130.5262   $130.53   $130.55   $130.50  
  Purchase #4 $35.63   11.260%   $39.6419   $39.64   $39.65   $39.60  
  Purchase #5 $68.82   10.648%   $76.148   $76.15   $76.15   $76.10  
  Purchase #6 $47.47   8.218%   $51.3711   $51.37   $51.35   $51.40  
  Purchase #7 $202.81   3.111%   $209.1194   $209.12   $209.10   $209.10  
  7 purchase totals = $907.11       $976.7423   $976.75   $976.75   $976.60