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 $60.54   6.195%   $64.2905   $64.29   $64.30   $64.30  
  Purchase #2 $160.41   13.535%   $182.1215   $182.12   $182.10   $182.10  
  Purchase #3 $112.38   3.335%   $116.1279   $116.13   $116.15   $116.10  
  Purchase #4 $48.80   12.485%   $54.8927   $54.89   $54.90   $54.90  
  Purchase #5 $88.95   8.117%   $96.1701   $96.17   $96.15   $96.20  
  Purchase #6 $247.72   8.784%   $269.4797   $269.48   $269.50   $269.50  
  Purchase #7 $179.97   13.734%   $204.6871   $204.69   $204.70   $204.70  
  7 purchase totals = $898.77       $987.7695   $987.77   $987.80   $987.80