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 $130.28   4.858%   $136.609   $136.61   $136.60   $136.60  
  Purchase #2 $37.65   9.248%   $41.1319   $41.13   $41.15   $41.10  
  Purchase #3 $151.83   4.829%   $159.1619   $159.16   $159.15   $159.20  
  Purchase #4 $66.86   9.629%   $73.2979   $73.30   $73.30   $73.30  
  Purchase #5 $159.79   5.544%   $168.6488   $168.65   $168.65   $168.60  
  Purchase #6 $84.56   9.663%   $92.731   $92.73   $92.75   $92.70  
  Purchase #7 $74.36   9.447%   $81.3848   $81.38   $81.40   $81.40  
  7 purchase totals = $705.33       $752.9653   $752.96   $753.00   $752.90