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 $85.75   9.153%   $93.5987   $93.60   $93.60   $93.60  
  Purchase #2 $142.48   9.330%   $155.7734   $155.77   $155.75   $155.80  
  Purchase #3 $224.69   9.420%   $245.8558   $245.86   $245.85   $245.90  
  Purchase #4 $154.64   3.321%   $159.7756   $159.78   $159.80   $159.80  
  Purchase #5 $26.60   3.797%   $27.61   $27.61   $27.60   $27.60  
  Purchase #6 $14.99   4.423%   $15.653   $15.65   $15.65   $15.70  
  Purchase #7 $67.98   7.625%   $73.1635   $73.16   $73.15   $73.20  
  7 purchase totals = $717.13       $771.4300   $771.43   $771.40   $771.60