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 $195.97   10.309%   $216.1725   $216.17   $216.15   $216.20  
  Purchase #2 $98.75   6.211%   $104.8834   $104.88   $104.90   $104.90  
  Purchase #3 $34.51   7.290%   $37.0258   $37.03   $37.05   $37.00  
  Purchase #4 $22.80   13.215%   $25.813   $25.81   $25.80   $25.80  
  Purchase #5 $56.59   13.134%   $64.0225   $64.02   $64.00   $64.00  
  Purchase #6 $162.41   13.648%   $184.5757   $184.58   $184.60   $184.60  
  Purchase #7 $53.80   8.583%   $58.4177   $58.42   $58.40   $58.40  
  7 purchase totals = $624.83       $690.9106   $690.91   $690.90   $690.90