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 $96.48   5.308%   $101.6012   $101.60   $101.60   $101.60  
  Purchase #2 $182.65   5.581%   $192.8437   $192.84   $192.85   $192.80  
  Purchase #3 $152.40   13.813%   $173.451   $173.45   $173.45   $173.50  
  Purchase #4 $61.54   7.624%   $66.2318   $66.23   $66.25   $66.20  
  Purchase #5 $73.73   4.698%   $77.1938   $77.19   $77.20   $77.20  
  Purchase #6 $17.29   7.377%   $18.5655   $18.57   $18.55   $18.60  
  Purchase #7 $156.47   5.447%   $164.9929   $164.99   $165.00   $165.00  
  7 purchase totals = $740.56       $794.8799   $794.87   $794.90   $794.90