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 $183.68   10.383%   $202.7515   $202.75   $202.75   $202.80  
  Purchase #2 $125.38   6.117%   $133.0495   $133.05   $133.05   $133.00  
  Purchase #3 $18.77   13.327%   $21.2715   $21.27   $21.25   $21.30  
  Purchase #4 $167.72   11.155%   $186.4292   $186.43   $186.45   $186.40  
  Purchase #5 $194.84   3.473%   $201.6068   $201.61   $201.60   $201.60  
  Purchase #6 $5.98   8.746%   $6.503   $6.50   $6.50   $6.50  
  Purchase #7 $230.53   13.541%   $261.7461   $261.75   $261.75   $261.70  
  7 purchase totals = $926.90       $1,013.3576   $1,013.36   $1,013.35   $1,013.30