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 $225.87   10.670%   $249.9703   $249.97   $249.95   $250.00  
  Purchase #2 $60.28   8.590%   $65.4581   $65.46   $65.45   $65.50  
  Purchase #3 $167.35   3.484%   $173.1805   $173.18   $173.20   $173.20  
  Purchase #4 $103.68   11.636%   $115.7442   $115.74   $115.75   $115.70  
  Purchase #5 $154.58   8.497%   $167.7147   $167.71   $167.70   $167.70  
  Purchase #6 $62.34   7.361%   $66.9288   $66.93   $66.95   $66.90  
  Purchase #7 $209.99   8.469%   $227.7741   $227.77   $227.75   $227.80  
  7 purchase totals = $984.09       $1,066.7707   $1,066.76   $1,066.75   $1,066.80