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 $243.48   9.513%   $266.6423   $266.64   $266.65   $266.60  
  Purchase #2 $159.51   8.841%   $173.6123   $173.61   $173.60   $173.60  
  Purchase #3 $171.38   10.136%   $188.7511   $188.75   $188.75   $188.80  
  Purchase #4 $73.84   13.630%   $83.9044   $83.90   $83.90   $83.90  
  Purchase #5 $15.93   4.473%   $16.6425   $16.64   $16.65   $16.60  
  Purchase #6 $192.95   3.148%   $199.0241   $199.02   $199.00   $199.00  
  Purchase #7 $62.62   5.872%   $66.297   $66.30   $66.30   $66.30  
  7 purchase totals = $919.71       $994.8737   $994.86   $994.85   $994.80