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 $92.34   9.496%   $101.1086   $101.11   $101.10   $101.10  
  Purchase #2 $239.80   8.446%   $260.0535   $260.05   $260.05   $260.10  
  Purchase #3 $5.93   4.381%   $6.1898   $6.19   $6.20   $6.20  
  Purchase #4 $42.72   9.847%   $46.9266   $46.93   $46.95   $46.90  
  Purchase #5 $155.47   5.161%   $163.4938   $163.49   $163.50   $163.50  
  Purchase #6 $184.66   5.677%   $195.1431   $195.14   $195.15   $195.10  
  Purchase #7 $182.92   7.306%   $196.2841   $196.28   $196.30   $196.30  
  7 purchase totals = $903.84       $969.1995   $969.19   $969.25   $969.20