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 $23.98   3.147%   $24.7347   $24.73   $24.75   $24.70  
  Purchase #2 $173.33   5.113%   $182.1924   $182.19   $182.20   $182.20  
  Purchase #3 $240.67   10.721%   $266.4722   $266.47   $266.45   $266.50  
  Purchase #4 $147.99   7.103%   $158.5017   $158.50   $158.50   $158.50  
  Purchase #5 $23.71   3.735%   $24.5956   $24.60   $24.60   $24.60  
  Purchase #6 $223.67   11.791%   $250.0429   $250.04   $250.05   $250.00  
  Purchase #7 $202.92   12.265%   $227.8081   $227.81   $227.80   $227.80  
  7 purchase totals = $1,036.27       $1,134.3476   $1,134.34   $1,134.35   $1,134.30