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 $96.69   8.874%   $105.2703   $105.27   $105.25   $105.30  
  Purchase #2 $85.35   13.213%   $96.6273   $96.63   $96.65   $96.60  
  Purchase #3 $91.25   4.390%   $95.2559   $95.26   $95.25   $95.30  
  Purchase #4 $225.34   8.755%   $245.0685   $245.07   $245.05   $245.10  
  Purchase #5 $113.71   10.128%   $125.2265   $125.23   $125.25   $125.20  
  Purchase #6 $132.84   3.443%   $137.4137   $137.41   $137.40   $137.40  
  Purchase #7 $215.79   9.255%   $235.7614   $235.76   $235.75   $235.80  
  7 purchase totals = $960.97       $1,040.6236   $1,040.63   $1,040.60   $1,040.70