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 $218.62   8.716%   $237.6749   $237.67   $237.65   $237.70  
  Purchase #2 $14.43   9.217%   $15.76   $15.76   $15.75   $15.80  
  Purchase #3 $92.46   11.855%   $103.4211   $103.42   $103.40   $103.40  
  Purchase #4 $207.86   7.863%   $224.204   $224.20   $224.20   $224.20  
  Purchase #5 $126.75   7.767%   $136.5947   $136.59   $136.60   $136.60  
  Purchase #6 $183.74   13.513%   $208.5688   $208.57   $208.55   $208.60  
  Purchase #7 $5.63   8.612%   $6.1149   $6.11   $6.10   $6.10  
  7 purchase totals = $849.49       $932.3384   $932.32   $932.25   $932.40