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 $62.68   5.307%   $66.0064   $66.01   $66.00   $66.00  
  Purchase #2 $106.44   4.242%   $110.9552   $110.96   $110.95   $111.00  
  Purchase #3 $82.82   3.152%   $85.4305   $85.43   $85.45   $85.40  
  Purchase #4 $154.99   13.539%   $175.9741   $175.97   $175.95   $176.00  
  Purchase #5 $88.38   10.558%   $97.7112   $97.71   $97.70   $97.70  
  Purchase #6 $225.89   8.462%   $245.0048   $245.00   $245.00   $245.00  
  Purchase #7 $101.50   6.644%   $108.2437   $108.24   $108.25   $108.20  
  7 purchase totals = $822.70       $889.3259   $889.32   $889.30   $889.30