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 $119.43   11.640%   $133.3317   $133.33   $133.35   $133.30  
  Purchase #2 $107.48   6.651%   $114.6285   $114.63   $114.65   $114.60  
  Purchase #3 $46.38   6.107%   $49.2124   $49.21   $49.20   $49.20  
  Purchase #4 $199.96   7.220%   $214.3971   $214.40   $214.40   $214.40  
  Purchase #5 $234.87   10.328%   $259.1274   $259.13   $259.15   $259.10  
  Purchase #6 $229.75   6.735%   $245.2237   $245.22   $245.20   $245.20  
  Purchase #7 $213.33   9.775%   $234.183   $234.18   $234.20   $234.20  
  7 purchase totals = $1,151.20       $1,250.1038   $1,250.10   $1,250.15   $1,250.00