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 $57.88   6.237%   $61.49   $61.49   $61.50   $61.50  
  Purchase #2 $31.59   3.611%   $32.7307   $32.73   $32.75   $32.70  
  Purchase #3 $168.34   5.413%   $177.4522   $177.45   $177.45   $177.50  
  Purchase #4 $24.90   11.221%   $27.694   $27.69   $27.70   $27.70  
  Purchase #5 $208.30   4.284%   $217.2236   $217.22   $217.20   $217.20  
  Purchase #6 $163.63   7.133%   $175.3017   $175.30   $175.30   $175.30  
  Purchase #7 $107.27   11.374%   $119.4709   $119.47   $119.45   $119.50  
  7 purchase totals = $761.91       $811.3631   $811.35   $811.35   $811.40