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 $236.25   8.619%   $256.6124   $256.61   $256.60   $256.60  
  Purchase #2 $73.28   11.613%   $81.79   $81.79   $81.80   $81.80  
  Purchase #3 $218.63   3.183%   $225.589   $225.59   $225.60   $225.60  
  Purchase #4 $122.54   3.150%   $126.4   $126.40   $126.40   $126.40  
  Purchase #5 $28.27   4.844%   $29.6394   $29.64   $29.65   $29.60  
  Purchase #6 $20.90   10.381%   $23.0696   $23.07   $23.05   $23.10  
  Purchase #7 $204.60   5.497%   $215.8469   $215.85   $215.85   $215.80  
  7 purchase totals = $904.47       $958.9473   $958.95   $958.95   $958.90