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 $57.28   8.253%   $62.0073   $62.01   $62.00   $62.00  
  Purchase #2 $151.95   5.226%   $159.8909   $159.89   $159.90   $159.90  
  Purchase #3 $106.77   3.474%   $110.4792   $110.48   $110.50   $110.50  
  Purchase #4 $82.87   5.656%   $87.5571   $87.56   $87.55   $87.60  
  Purchase #5 $92.77   4.596%   $97.0337   $97.03   $97.05   $97.00  
  Purchase #6 $232.99   12.148%   $261.2936   $261.29   $261.30   $261.30  
  Purchase #7 $109.41   6.441%   $116.4571   $116.46   $116.45   $116.50  
  7 purchase totals = $834.04       $894.7189   $894.72   $894.75   $894.80