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 $91.36   7.541%   $98.2495   $98.25   $98.25   $98.20  
  Purchase #2 $62.81   9.443%   $68.7411   $68.74   $68.75   $68.70  
  Purchase #3 $60.40   10.327%   $66.6375   $66.64   $66.65   $66.60  
  Purchase #4 $245.72   6.288%   $261.1709   $261.17   $261.15   $261.20  
  Purchase #5 $229.45   4.569%   $239.9336   $239.93   $239.95   $239.90  
  Purchase #6 $27.25   9.300%   $29.7843   $29.78   $29.80   $29.80  
  Purchase #7 $238.72   6.696%   $254.7047   $254.70   $254.70   $254.70  
  7 purchase totals = $955.71       $1,019.2216   $1,019.21   $1,019.25   $1,019.10