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 $233.84   13.732%   $265.9509   $265.95   $265.95   $266.00  
  Purchase #2 $60.31   9.676%   $66.1456   $66.15   $66.15   $66.10  
  Purchase #3 $209.36   9.842%   $229.9652   $229.97   $229.95   $230.00  
  Purchase #4 $98.38   5.416%   $103.7083   $103.71   $103.70   $103.70  
  Purchase #5 $239.78   8.305%   $259.6937   $259.69   $259.70   $259.70  
  Purchase #6 $140.74   11.819%   $157.3741   $157.37   $157.35   $157.40  
  Purchase #7 $64.65   6.163%   $68.6344   $68.63   $68.65   $68.60  
  7 purchase totals = $1,047.06       $1,151.4722   $1,151.47   $1,151.45   $1,151.50