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 $246.76   11.104%   $274.1602   $274.16   $274.15   $274.20  
  Purchase #2 $236.38   8.351%   $256.1201   $256.12   $256.10   $256.10  
  Purchase #3 $114.43   4.591%   $119.6835   $119.68   $119.70   $119.70  
  Purchase #4 $101.47   11.108%   $112.7413   $112.74   $112.75   $112.70  
  Purchase #5 $127.82   7.175%   $136.9911   $136.99   $137.00   $137.00  
  Purchase #6 $169.53   10.703%   $187.6748   $187.67   $187.65   $187.70  
  Purchase #7 $44.92   3.297%   $46.401   $46.40   $46.40   $46.40  
  7 purchase totals = $1,041.31       $1,133.7720   $1,133.76   $1,133.75   $1,133.80