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 $234.79   10.756%   $260.044   $260.04   $260.05   $260.00  
  Purchase #2 $53.32   7.556%   $57.3489   $57.35   $57.35   $57.30  
  Purchase #3 $229.47   10.346%   $253.211   $253.21   $253.20   $253.20  
  Purchase #4 $5.77   4.808%   $6.0474   $6.05   $6.05   $6.00  
  Purchase #5 $139.66   3.394%   $144.4001   $144.40   $144.40   $144.40  
  Purchase #6 $167.69   5.667%   $177.193   $177.19   $177.20   $177.20  
  Purchase #7 $54.30   5.102%   $57.0704   $57.07   $57.05   $57.10  
  7 purchase totals = $885.00       $955.3148   $955.31   $955.30   $955.20