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 $247.72   7.451%   $266.1776   $266.18   $266.20   $266.20  
  Purchase #2 $56.86   6.389%   $60.4928   $60.49   $60.50   $60.50  
  Purchase #3 $58.45   9.817%   $64.188   $64.19   $64.20   $64.20  
  Purchase #4 $79.95   10.419%   $88.28   $88.28   $88.30   $88.30  
  Purchase #5 $170.80   4.870%   $179.118   $179.12   $179.10   $179.10  
  Purchase #6 $187.89   13.163%   $212.622   $212.62   $212.60   $212.60  
  Purchase #7 $94.35   9.857%   $103.6501   $103.65   $103.65   $103.70  
  7 purchase totals = $896.02       $974.5285   $974.53   $974.55   $974.60