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 $228.90   3.182%   $236.1836   $236.18   $236.20   $236.20  
  Purchase #2 $56.65   5.213%   $59.6032   $59.60   $59.60   $59.60  
  Purchase #3 $142.40   8.106%   $153.9429   $153.94   $153.95   $153.90  
  Purchase #4 $67.59   4.394%   $70.5599   $70.56   $70.55   $70.60  
  Purchase #5 $205.63   13.361%   $233.1042   $233.10   $233.10   $233.10  
  Purchase #6 $75.35   11.741%   $84.1968   $84.20   $84.20   $84.20  
  Purchase #7 $22.53   11.772%   $25.1822   $25.18   $25.20   $25.20  
  7 purchase totals = $799.05       $862.7728   $862.76   $862.80   $862.80