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 $61.61   12.503%   $69.3131   $69.31   $69.30   $69.30  
  Purchase #2 $195.69   6.285%   $207.9891   $207.99   $208.00   $208.00  
  Purchase #3 $46.49   10.105%   $51.1878   $51.19   $51.20   $51.20  
  Purchase #4 $160.88   11.193%   $178.8873   $178.89   $178.90   $178.90  
  Purchase #5 $161.52   13.612%   $183.5061   $183.51   $183.50   $183.50  
  Purchase #6 $72.42   4.292%   $75.5283   $75.53   $75.55   $75.50  
  Purchase #7 $83.38   3.861%   $86.5993   $86.60   $86.60   $86.60  
  7 purchase totals = $781.99       $853.0110   $853.02   $853.05   $853.00