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 $83.68   5.518%   $88.2975   $88.30   $88.30   $88.30  
  Purchase #2 $93.40   4.399%   $97.5087   $97.51   $97.50   $97.50  
  Purchase #3 $85.36   5.591%   $90.1325   $90.13   $90.15   $90.10  
  Purchase #4 $202.69   5.724%   $214.292   $214.29   $214.30   $214.30  
  Purchase #5 $47.36   9.660%   $51.935   $51.94   $51.95   $51.90  
  Purchase #6 $209.27   7.273%   $224.4902   $224.49   $224.50   $224.50  
  Purchase #7 $24.57   4.665%   $25.7162   $25.72   $25.70   $25.70  
  7 purchase totals = $746.33       $792.3721   $792.38   $792.40   $792.30