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 $133.69   12.730%   $150.7087   $150.71   $150.70   $150.70  
  Purchase #2 $5.71   10.725%   $6.3224   $6.32   $6.30   $6.30  
  Purchase #3 $61.54   5.585%   $64.977   $64.98   $65.00   $65.00  
  Purchase #4 $235.46   12.243%   $264.2874   $264.29   $264.30   $264.30  
  Purchase #5 $106.26   12.484%   $119.5255   $119.53   $119.55   $119.50  
  Purchase #6 $129.34   10.465%   $142.8754   $142.88   $142.90   $142.90  
  Purchase #7 $199.63   4.855%   $209.322   $209.32   $209.30   $209.30  
  7 purchase totals = $871.63       $958.0184   $958.03   $958.05   $958.00