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 $53.58   12.348%   $60.1961   $60.20   $60.20   $60.20  
  Purchase #2 $117.87   6.782%   $125.8639   $125.86   $125.85   $125.90  
  Purchase #3 $201.41   11.578%   $224.7292   $224.73   $224.75   $224.70  
  Purchase #4 $13.67   8.646%   $14.8519   $14.85   $14.85   $14.90  
  Purchase #5 $198.78   9.484%   $217.6323   $217.63   $217.65   $217.60  
  Purchase #6 $243.97   7.781%   $262.9533   $262.95   $262.95   $263.00  
  Purchase #7 $38.97   9.840%   $42.8046   $42.80   $42.80   $42.80  
  7 purchase totals = $868.25       $949.0313   $949.02   $949.05   $949.10