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 $89.57   8.226%   $96.938   $96.94   $96.95   $96.90  
  Purchase #2 $129.79   5.122%   $136.4378   $136.44   $136.45   $136.40  
  Purchase #3 $130.34   10.213%   $143.6516   $143.65   $143.65   $143.70  
  Purchase #4 $114.85   12.499%   $129.2051   $129.21   $129.20   $129.20  
  Purchase #5 $208.38   6.226%   $221.3537   $221.35   $221.35   $221.40  
  Purchase #6 $16.33   3.616%   $16.9205   $16.92   $16.90   $16.90  
  Purchase #7 $250.87   11.560%   $279.8706   $279.87   $279.85   $279.90  
  7 purchase totals = $940.13       $1,024.3773   $1,024.38   $1,024.35   $1,024.40