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 $72.46   5.640%   $76.5467   $76.55   $76.55   $76.50  
  Purchase #2 $231.89   12.632%   $261.1823   $261.18   $261.20   $261.20  
  Purchase #3 $115.54   12.138%   $129.5642   $129.56   $129.55   $129.60  
  Purchase #4 $87.31   11.368%   $97.2354   $97.24   $97.25   $97.20  
  Purchase #5 $167.33   4.171%   $174.3093   $174.31   $174.30   $174.30  
  Purchase #6 $41.31   8.658%   $44.8866   $44.89   $44.90   $44.90  
  Purchase #7 $202.49   3.708%   $209.9983   $210.00   $210.00   $210.00  
  7 purchase totals = $918.33       $993.7228   $993.73   $993.75   $993.70