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 $227.92   12.552%   $256.5285   $256.53   $256.55   $256.50  
  Purchase #2 $175.62   10.490%   $194.0425   $194.04   $194.05   $194.00  
  Purchase #3 $44.57   12.139%   $49.9804   $49.98   $50.00   $50.00  
  Purchase #4 $65.77   13.279%   $74.5036   $74.50   $74.50   $74.50  
  Purchase #5 $199.48   8.337%   $216.1106   $216.11   $216.10   $216.10  
  Purchase #6 $221.54   3.473%   $229.2341   $229.23   $229.25   $229.20  
  Purchase #7 $216.34   12.303%   $242.9563   $242.96   $242.95   $243.00  
  7 purchase totals = $1,151.24       $1,263.3560   $1,263.35   $1,263.40   $1,263.30