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 $223.63   10.299%   $246.6617   $246.66   $246.65   $246.70  
  Purchase #2 $62.47   9.386%   $68.3334   $68.33   $68.35   $68.30  
  Purchase #3 $229.63   10.395%   $253.5   $253.50   $253.50   $253.50  
  Purchase #4 $33.53   12.406%   $37.6897   $37.69   $37.70   $37.70  
  Purchase #5 $44.76   8.674%   $48.6425   $48.64   $48.65   $48.60  
  Purchase #6 $223.61   12.766%   $252.1561   $252.16   $252.15   $252.20  
  Purchase #7 $39.74   7.628%   $42.7714   $42.77   $42.75   $42.80  
  7 purchase totals = $857.37       $949.7548   $949.75   $949.75   $949.80