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 $239.86   5.600%   $253.2922   $253.29   $253.30   $253.30  
  Purchase #2 $87.79   8.280%   $95.059   $95.06   $95.05   $95.10  
  Purchase #3 $26.30   4.394%   $27.4556   $27.46   $27.45   $27.50  
  Purchase #4 $149.34   6.590%   $159.1815   $159.18   $159.20   $159.20  
  Purchase #5 $93.74   3.673%   $97.1831   $97.18   $97.20   $97.20  
  Purchase #6 $233.74   11.667%   $261.0104   $261.01   $261.00   $261.00  
  Purchase #7 $63.39   5.153%   $66.6565   $66.66   $66.65   $66.70  
  7 purchase totals = $894.16       $959.8383   $959.84   $959.85   $960.00