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 $58.94   7.783%   $63.5273   $63.53   $63.55   $63.50  
  Purchase #2 $94.69   8.255%   $102.5067   $102.51   $102.50   $102.50  
  Purchase #3 $195.93   3.677%   $203.1343   $203.13   $203.15   $203.10  
  Purchase #4 $151.99   11.572%   $169.5783   $169.58   $169.60   $169.60  
  Purchase #5 $205.81   10.355%   $227.1216   $227.12   $227.10   $227.10  
  Purchase #6 $104.33   9.392%   $114.1287   $114.13   $114.15   $114.10  
  Purchase #7 $60.92   12.321%   $68.426   $68.43   $68.45   $68.40  
  7 purchase totals = $872.61       $948.4229   $948.43   $948.50   $948.30