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 $101.74   11.562%   $113.5032   $113.50   $113.50   $113.50  
  Purchase #2 $55.61   9.369%   $60.8201   $60.82   $60.80   $60.80  
  Purchase #3 $114.54   9.760%   $125.7191   $125.72   $125.70   $125.70  
  Purchase #4 $206.95   8.667%   $224.8864   $224.89   $224.90   $224.90  
  Purchase #5 $229.66   10.596%   $253.9948   $253.99   $254.00   $254.00  
  Purchase #6 $25.87   6.599%   $27.5772   $27.58   $27.60   $27.60  
  Purchase #7 $151.56   11.575%   $169.1031   $169.10   $169.10   $169.10  
  7 purchase totals = $885.93       $975.6039   $975.60   $975.60   $975.60