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 $24.40   13.313%   $27.6484   $27.65   $27.65   $27.60  
  Purchase #2 $236.99   12.745%   $267.1944   $267.19   $267.20   $267.20  
  Purchase #3 $116.97   12.771%   $131.9082   $131.91   $131.90   $131.90  
  Purchase #4 $49.25   4.422%   $51.4278   $51.43   $51.45   $51.40  
  Purchase #5 $69.91   13.637%   $79.4436   $79.44   $79.45   $79.40  
  Purchase #6 $71.74   4.192%   $74.7473   $74.75   $74.75   $74.70  
  Purchase #7 $152.41   5.712%   $161.1157   $161.12   $161.10   $161.10  
  7 purchase totals = $721.67       $793.4854   $793.49   $793.50   $793.30