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 $232.65   10.481%   $257.034   $257.03   $257.05   $257.00  
  Purchase #2 $5.34   13.127%   $6.041   $6.04   $6.05   $6.00  
  Purchase #3 $30.91   5.813%   $32.7068   $32.71   $32.70   $32.70  
  Purchase #4 $60.85   9.149%   $66.4172   $66.42   $66.40   $66.40  
  Purchase #5 $159.95   3.703%   $165.8729   $165.87   $165.85   $165.90  
  Purchase #6 $160.79   9.748%   $176.4638   $176.46   $176.45   $176.50  
  Purchase #7 $140.33   12.403%   $157.7351   $157.74   $157.75   $157.70  
  7 purchase totals = $790.82       $862.2708   $862.27   $862.25   $862.20