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 $106.81   12.119%   $119.7543   $119.75   $119.75   $119.80  
  Purchase #2 $242.74   13.353%   $275.1531   $275.15   $275.15   $275.20  
  Purchase #3 $245.41   13.170%   $277.7305   $277.73   $277.75   $277.70  
  Purchase #4 $245.96   12.497%   $276.6976   $276.70   $276.70   $276.70  
  Purchase #5 $47.39   9.569%   $51.9247   $51.92   $51.90   $51.90  
  Purchase #6 $198.39   13.780%   $225.7281   $225.73   $225.75   $225.70  
  Purchase #7 $203.44   11.399%   $226.6301   $226.63   $226.65   $226.60  
  7 purchase totals = $1,290.14       $1,453.6184   $1,453.61   $1,453.65   $1,453.60