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 $45.98   6.519%   $48.9774   $48.98   $49.00   $49.00  
  Purchase #2 $214.55   4.535%   $224.2798   $224.28   $224.30   $224.30  
  Purchase #3 $195.32   13.583%   $221.8503   $221.85   $221.85   $221.90  
  Purchase #4 $226.39   9.655%   $248.248   $248.25   $248.25   $248.20  
  Purchase #5 $102.84   10.607%   $113.7482   $113.75   $113.75   $113.70  
  Purchase #6 $68.62   3.420%   $70.9668   $70.97   $70.95   $71.00  
  Purchase #7 $38.25   11.488%   $42.6442   $42.64   $42.65   $42.60  
  7 purchase totals = $891.95       $970.7147   $970.72   $970.75   $970.70