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 $33.75   3.416%   $34.9029   $34.90   $34.90   $34.90  
  Purchase #2 $127.84   10.349%   $141.0702   $141.07   $141.05   $141.10  
  Purchase #3 $61.49   5.201%   $64.6881   $64.69   $64.70   $64.70  
  Purchase #4 $240.60   3.660%   $249.406   $249.41   $249.40   $249.40  
  Purchase #5 $120.55   13.572%   $136.911   $136.91   $136.90   $136.90  
  Purchase #6 $44.65   5.612%   $47.1558   $47.16   $47.15   $47.20  
  Purchase #7 $199.66   8.857%   $217.3439   $217.34   $217.35   $217.30  
  7 purchase totals = $828.54       $891.4779   $891.48   $891.45   $891.50