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 $44.55   3.338%   $46.0371   $46.04   $46.05   $46.00  
  Purchase #2 $241.64   9.466%   $264.5136   $264.51   $264.50   $264.50  
  Purchase #3 $236.37   3.630%   $244.9502   $244.95   $244.95   $245.00  
  Purchase #4 $213.89   4.379%   $223.2562   $223.26   $223.25   $223.30  
  Purchase #5 $227.45   9.119%   $248.1912   $248.19   $248.20   $248.20  
  Purchase #6 $200.75   3.577%   $207.9308   $207.93   $207.95   $207.90  
  Purchase #7 $97.69   5.441%   $103.0053   $103.01   $103.00   $103.00  
  7 purchase totals = $1,262.34       $1,337.8844   $1,337.89   $1,337.90   $1,337.90