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 $59.99   3.386%   $62.0213   $62.02   $62.00   $62.00  
  Purchase #2 $104.34   11.444%   $116.2807   $116.28   $116.30   $116.30  
  Purchase #3 $77.87   5.176%   $81.9006   $81.90   $81.90   $81.90  
  Purchase #4 $66.32   13.370%   $75.187   $75.19   $75.20   $75.20  
  Purchase #5 $240.85   5.335%   $253.6993   $253.70   $253.70   $253.70  
  Purchase #6 $35.85   11.761%   $40.0663   $40.07   $40.05   $40.10  
  Purchase #7 $67.65   8.277%   $73.2494   $73.25   $73.25   $73.20  
  7 purchase totals = $652.87       $702.4046   $702.41   $702.40   $702.40