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 $195.94   6.582%   $208.8368   $208.84   $208.85   $208.80  
  Purchase #2 $157.81   8.834%   $171.7509   $171.75   $171.75   $171.80  
  Purchase #3 $36.27   13.551%   $41.1849   $41.18   $41.20   $41.20  
  Purchase #4 $154.30   4.650%   $161.475   $161.48   $161.50   $161.50  
  Purchase #5 $207.88   7.416%   $223.2964   $223.30   $223.30   $223.30  
  Purchase #6 $26.29   10.402%   $29.0247   $29.02   $29.00   $29.00  
  Purchase #7 $67.90   3.298%   $70.1393   $70.14   $70.15   $70.10  
  7 purchase totals = $846.39       $905.7080   $905.71   $905.75   $905.70