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 $219.41   11.389%   $244.3986   $244.40   $244.40   $244.40  
  Purchase #2 $228.85   9.550%   $250.7052   $250.71   $250.70   $250.70  
  Purchase #3 $17.75   4.630%   $18.5718   $18.57   $18.55   $18.60  
  Purchase #4 $162.51   9.785%   $178.4116   $178.41   $178.40   $178.40  
  Purchase #5 $64.79   5.371%   $68.2699   $68.27   $68.25   $68.30  
  Purchase #6 $218.82   8.262%   $236.8989   $236.90   $236.90   $236.90  
  Purchase #7 $68.33   11.810%   $76.3998   $76.40   $76.40   $76.40  
  7 purchase totals = $980.46       $1,073.6558   $1,073.66   $1,073.60   $1,073.70