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 $54.66   13.753%   $62.1774   $62.18   $62.20   $62.20  
  Purchase #2 $205.54   7.422%   $220.7952   $220.80   $220.80   $220.80  
  Purchase #3 $54.76   5.210%   $57.613   $57.61   $57.60   $57.60  
  Purchase #4 $227.79   3.671%   $236.1522   $236.15   $236.15   $236.20  
  Purchase #5 $92.98   5.428%   $98.027   $98.03   $98.05   $98.00  
  Purchase #6 $14.46   12.479%   $16.2645   $16.26   $16.25   $16.30  
  Purchase #7 $120.78   6.563%   $128.7068   $128.71   $128.70   $128.70  
  7 purchase totals = $770.97       $819.7361   $819.74   $819.75   $819.80