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 $83.29   11.141%   $92.5693   $92.57   $92.55   $92.60  
  Purchase #2 $172.54   13.348%   $195.5706   $195.57   $195.55   $195.60  
  Purchase #3 $214.92   13.639%   $244.2329   $244.23   $244.25   $244.20  
  Purchase #4 $248.37   12.523%   $279.4734   $279.47   $279.45   $279.50  
  Purchase #5 $128.93   8.311%   $139.6454   $139.65   $139.65   $139.60  
  Purchase #6 $119.79   4.104%   $124.7062   $124.71   $124.70   $124.70  
  Purchase #7 $40.89   8.368%   $44.3117   $44.31   $44.30   $44.30  
  7 purchase totals = $1,008.73       $1,120.5095   $1,120.51   $1,120.45   $1,120.50