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 $52.42   9.181%   $57.2327   $57.23   $57.25   $57.20  
  Purchase #2 $141.61   13.229%   $160.3436   $160.34   $160.35   $160.30  
  Purchase #3 $185.82   9.177%   $202.8727   $202.87   $202.85   $202.90  
  Purchase #4 $16.72   4.698%   $17.5055   $17.51   $17.50   $17.50  
  Purchase #5 $174.74   12.131%   $195.9377   $195.94   $195.95   $195.90  
  Purchase #6 $58.37   11.870%   $65.2985   $65.30   $65.30   $65.30  
  Purchase #7 $144.69   5.709%   $152.9504   $152.95   $152.95   $153.00  
  7 purchase totals = $774.37       $852.1411   $852.14   $852.15   $852.10