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 $237.67   4.867%   $249.2374   $249.24   $249.25   $249.20  
  Purchase #2 $108.29   8.543%   $117.5412   $117.54   $117.55   $117.50  
  Purchase #3 $41.83   5.579%   $44.1637   $44.16   $44.15   $44.20  
  Purchase #4 $31.86   5.388%   $33.5766   $33.58   $33.60   $33.60  
  Purchase #5 $40.42   4.777%   $42.3509   $42.35   $42.35   $42.40  
  Purchase #6 $188.51   5.768%   $199.3833   $199.38   $199.40   $199.40  
  Purchase #7 $43.39   6.842%   $46.3587   $46.36   $46.35   $46.40  
  7 purchase totals = $691.97       $732.6118   $732.61   $732.65   $732.70