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 $213.71   12.175%   $239.7292   $239.73   $239.75   $239.70  
  Purchase #2 $92.70   11.681%   $103.5283   $103.53   $103.55   $103.50  
  Purchase #3 $10.58   10.799%   $11.7225   $11.72   $11.70   $11.70  
  Purchase #4 $153.58   5.179%   $161.5339   $161.53   $161.55   $161.50  
  Purchase #5 $245.40   6.539%   $261.4467   $261.45   $261.45   $261.40  
  Purchase #6 $149.97   10.165%   $165.2145   $165.21   $165.20   $165.20  
  Purchase #7 $119.43   7.465%   $128.3454   $128.35   $128.35   $128.30  
  7 purchase totals = $985.37       $1,071.5205   $1,071.52   $1,071.55   $1,071.30