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 $92.46   4.408%   $96.5356   $96.54   $96.55   $96.50  
  Purchase #2 $221.71   10.298%   $244.5417   $244.54   $244.55   $244.50  
  Purchase #3 $103.59   9.818%   $113.7605   $113.76   $113.75   $113.80  
  Purchase #4 $229.74   8.212%   $248.6062   $248.61   $248.60   $248.60  
  Purchase #5 $199.58   11.554%   $222.6395   $222.64   $222.65   $222.60  
  Purchase #6 $8.29   6.299%   $8.8122   $8.81   $8.80   $8.80  
  Purchase #7 $44.66   5.817%   $47.2579   $47.26   $47.25   $47.30  
  7 purchase totals = $900.03       $982.1536   $982.16   $982.15   $982.10