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 $140.63   7.541%   $151.2349   $151.23   $151.25   $151.20  
  Purchase #2 $159.82   8.583%   $173.5374   $173.54   $173.55   $173.50  
  Purchase #3 $53.32   7.445%   $57.2897   $57.29   $57.30   $57.30  
  Purchase #4 $121.85   8.873%   $132.6618   $132.66   $132.65   $132.70  
  Purchase #5 $139.39   5.277%   $146.7456   $146.75   $146.75   $146.70  
  Purchase #6 $54.75   11.766%   $61.1919   $61.19   $61.20   $61.20  
  Purchase #7 $234.77   6.501%   $250.0324   $250.03   $250.05   $250.00  
  7 purchase totals = $904.53       $972.6937   $972.69   $972.75   $972.60