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 $114.47   9.166%   $124.9623   $124.96   $124.95   $125.00  
  Purchase #2 $75.30   4.107%   $78.3926   $78.39   $78.40   $78.40  
  Purchase #3 $217.58   11.792%   $243.237   $243.24   $243.25   $243.20  
  Purchase #4 $63.33   4.605%   $66.2463   $66.25   $66.25   $66.20  
  Purchase #5 $117.40   11.158%   $130.4995   $130.50   $130.50   $130.50  
  Purchase #6 $47.34   13.166%   $53.5728   $53.57   $53.55   $53.60  
  Purchase #7 $188.72   4.555%   $197.3162   $197.32   $197.30   $197.30  
  7 purchase totals = $824.14       $894.2267   $894.23   $894.20   $894.20