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 $91.62   5.586%   $96.7379   $96.74   $96.75   $96.70  
  Purchase #2 $57.96   7.594%   $62.3615   $62.36   $62.35   $62.40  
  Purchase #3 $179.39   3.241%   $185.204   $185.20   $185.20   $185.20  
  Purchase #4 $158.42   11.323%   $176.3579   $176.36   $176.35   $176.40  
  Purchase #5 $154.70   5.209%   $162.7583   $162.76   $162.75   $162.80  
  Purchase #6 $165.44   12.726%   $186.4939   $186.49   $186.50   $186.50  
  Purchase #7 $12.76   6.191%   $13.55   $13.55   $13.55   $13.60  
  7 purchase totals = $820.29       $883.4635   $883.46   $883.45   $883.60