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 $226.99   12.778%   $255.9948   $255.99   $256.00   $256.00  
  Purchase #2 $212.37   10.737%   $235.1722   $235.17   $235.15   $235.20  
  Purchase #3 $58.64   4.517%   $61.2888   $61.29   $61.30   $61.30  
  Purchase #4 $203.92   12.548%   $229.5079   $229.51   $229.50   $229.50  
  Purchase #5 $201.78   9.202%   $220.3478   $220.35   $220.35   $220.30  
  Purchase #6 $208.29   13.453%   $236.3113   $236.31   $236.30   $236.30  
  Purchase #7 $57.34   9.426%   $62.7449   $62.74   $62.75   $62.70  
  7 purchase totals = $1,169.33       $1,301.3677   $1,301.36   $1,301.35   $1,301.30