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 $104.90   3.546%   $108.6198   $108.62   $108.60   $108.60  
  Purchase #2 $105.47   13.349%   $119.5492   $119.55   $119.55   $119.50  
  Purchase #3 $148.71   8.667%   $161.5987   $161.60   $161.60   $161.60  
  Purchase #4 $133.92   7.662%   $144.181   $144.18   $144.20   $144.20  
  Purchase #5 $80.42   4.678%   $84.182   $84.18   $84.20   $84.20  
  Purchase #6 $227.48   5.134%   $239.1588   $239.16   $239.15   $239.20  
  Purchase #7 $151.85   8.466%   $164.7056   $164.71   $164.70   $164.70  
  7 purchase totals = $952.75       $1,021.9951   $1,022.00   $1,022.00   $1,022.00