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 $221.51   12.703%   $249.6484   $249.65   $249.65   $249.60  
  Purchase #2 $213.69   10.374%   $235.8582   $235.86   $235.85   $235.90  
  Purchase #3 $63.55   10.548%   $70.2533   $70.25   $70.25   $70.30  
  Purchase #4 $54.90   8.316%   $59.4655   $59.47   $59.45   $59.50  
  Purchase #5 $24.79   6.677%   $26.4452   $26.45   $26.45   $26.40  
  Purchase #6 $86.42   9.233%   $94.3992   $94.40   $94.40   $94.40  
  Purchase #7 $240.25   10.868%   $266.3604   $266.36   $266.35   $266.40  
  7 purchase totals = $905.11       $1,002.4302   $1,002.44   $1,002.40   $1,002.50