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 $64.89   12.785%   $73.1862   $73.19   $73.20   $73.20  
  Purchase #2 $117.80   7.274%   $126.3688   $126.37   $126.35   $126.40  
  Purchase #3 $210.75   8.320%   $228.2844   $228.28   $228.30   $228.30  
  Purchase #4 $242.47   10.852%   $268.7828   $268.78   $268.80   $268.80  
  Purchase #5 $21.54   3.339%   $22.2592   $22.26   $22.25   $22.30  
  Purchase #6 $53.34   8.504%   $57.876   $57.88   $57.90   $57.90  
  Purchase #7 $221.72   7.310%   $237.9277   $237.93   $237.95   $237.90  
  7 purchase totals = $932.51       $1,014.6851   $1,014.69   $1,014.75   $1,014.80