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 $60.33   12.795%   $68.0492   $68.05   $68.05   $68.00  
  Purchase #2 $47.43   7.319%   $50.9014   $50.90   $50.90   $50.90  
  Purchase #3 $44.55   13.245%   $50.4506   $50.45   $50.45   $50.50  
  Purchase #4 $192.86   10.548%   $213.2029   $213.20   $213.20   $213.20  
  Purchase #5 $208.78   11.743%   $233.297   $233.30   $233.30   $233.30  
  Purchase #6 $223.89   7.123%   $239.8377   $239.84   $239.85   $239.80  
  Purchase #7 $13.98   3.643%   $14.4893   $14.49   $14.50   $14.50  
  7 purchase totals = $791.82       $870.2281   $870.23   $870.25   $870.20