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 $231.94   7.283%   $248.8322   $248.83   $248.85   $248.80  
  Purchase #2 $188.41   3.689%   $195.3604   $195.36   $195.35   $195.40  
  Purchase #3 $141.63   6.770%   $151.2184   $151.22   $151.20   $151.20  
  Purchase #4 $174.85   7.189%   $187.42   $187.42   $187.40   $187.40  
  Purchase #5 $236.46   8.219%   $255.8946   $255.89   $255.90   $255.90  
  Purchase #6 $171.43   7.822%   $184.8393   $184.84   $184.85   $184.80  
  Purchase #7 $91.69   5.455%   $96.6917   $96.69   $96.70   $96.70  
  7 purchase totals = $1,236.41       $1,320.2566   $1,320.25   $1,320.25   $1,320.20