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 $216.99   8.227%   $234.8418   $234.84   $234.85   $234.80  
  Purchase #2 $88.55   10.846%   $98.1541   $98.15   $98.15   $98.20  
  Purchase #3 $176.75   6.829%   $188.8203   $188.82   $188.80   $188.80  
  Purchase #4 $95.56   13.235%   $108.2074   $108.21   $108.20   $108.20  
  Purchase #5 $229.62   8.870%   $249.9873   $249.99   $250.00   $250.00  
  Purchase #6 $79.44   13.235%   $89.9539   $89.95   $89.95   $90.00  
  Purchase #7 $76.75   3.347%   $79.3188   $79.32   $79.30   $79.30  
  7 purchase totals = $963.66       $1,049.2836   $1,049.28   $1,049.25   $1,049.30