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 $52.34   12.241%   $58.7469   $58.75   $58.75   $58.70  
  Purchase #2 $25.56   8.364%   $27.6978   $27.70   $27.70   $27.70  
  Purchase #3 $196.44   6.323%   $208.8609   $208.86   $208.85   $208.90  
  Purchase #4 $185.61   5.397%   $195.6274   $195.63   $195.65   $195.60  
  Purchase #5 $101.44   10.547%   $112.1389   $112.14   $112.15   $112.10  
  Purchase #6 $126.87   6.838%   $135.5454   $135.55   $135.55   $135.50  
  Purchase #7 $21.76   9.452%   $23.8168   $23.82   $23.80   $23.80  
  7 purchase totals = $710.02       $762.4341   $762.45   $762.45   $762.30