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 $106.44   6.423%   $113.2766   $113.28   $113.30   $113.30  
  Purchase #2 $68.68   8.545%   $74.5487   $74.55   $74.55   $74.50  
  Purchase #3 $9.49   7.842%   $10.2342   $10.23   $10.25   $10.20  
  Purchase #4 $196.40   5.205%   $206.6226   $206.62   $206.60   $206.60  
  Purchase #5 $149.53   12.765%   $168.6175   $168.62   $168.60   $168.60  
  Purchase #6 $155.59   4.298%   $162.2773   $162.28   $162.30   $162.30  
  Purchase #7 $57.77   6.538%   $61.547   $61.55   $61.55   $61.50  
  7 purchase totals = $743.90       $797.1239   $797.13   $797.15   $797.00