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 $157.30   11.841%   $175.9259   $175.93   $175.95   $175.90  
  Purchase #2 $239.63   9.287%   $261.8844   $261.88   $261.90   $261.90  
  Purchase #3 $87.45   10.345%   $96.4967   $96.50   $96.50   $96.50  
  Purchase #4 $125.25   8.314%   $135.6633   $135.66   $135.65   $135.70  
  Purchase #5 $210.36   12.587%   $236.838   $236.84   $236.85   $236.80  
  Purchase #6 $5.41   4.442%   $5.6503   $5.65   $5.65   $5.70  
  Purchase #7 $130.43   9.445%   $142.7491   $142.75   $142.75   $142.70  
  7 purchase totals = $955.83       $1,055.2077   $1,055.21   $1,055.25   $1,055.20