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 $208.48   13.172%   $235.941   $235.94   $235.95   $235.90  
  Purchase #2 $249.37   7.293%   $267.5566   $267.56   $267.55   $267.60  
  Purchase #3 $133.57   8.376%   $144.7578   $144.76   $144.75   $144.80  
  Purchase #4 $56.70   5.502%   $59.8196   $59.82   $59.80   $59.80  
  Purchase #5 $6.99   7.153%   $7.49   $7.49   $7.50   $7.50  
  Purchase #6 $36.69   12.539%   $41.2906   $41.29   $41.30   $41.30  
  Purchase #7 $127.98   9.422%   $140.0383   $140.04   $140.05   $140.00  
  7 purchase totals = $819.78       $896.8939   $896.90   $896.90   $896.90