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 $75.92   13.323%   $86.0348   $86.03   $86.05   $86.00  
  Purchase #2 $128.73   6.690%   $137.342   $137.34   $137.35   $137.30  
  Purchase #3 $78.86   7.578%   $84.836   $84.84   $84.85   $84.80  
  Purchase #4 $95.65   10.160%   $105.368   $105.37   $105.35   $105.40  
  Purchase #5 $81.46   7.870%   $87.8709   $87.87   $87.85   $87.90  
  Purchase #6 $180.60   8.448%   $195.8571   $195.86   $195.85   $195.90  
  Purchase #7 $229.79   13.443%   $260.6807   $260.68   $260.70   $260.70  
  7 purchase totals = $871.01       $957.9895   $957.99   $958.00   $958.00