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 $185.59   11.806%   $207.5008   $207.50   $207.50   $207.50  
  Purchase #2 $240.45   6.854%   $256.9304   $256.93   $256.95   $256.90  
  Purchase #3 $87.43   3.377%   $90.3825   $90.38   $90.40   $90.40  
  Purchase #4 $216.86   9.452%   $237.3576   $237.36   $237.35   $237.40  
  Purchase #5 $208.73   11.758%   $233.2725   $233.27   $233.25   $233.30  
  Purchase #6 $5.63   5.318%   $5.9294   $5.93   $5.95   $5.90  
  Purchase #7 $249.91   9.349%   $273.2741   $273.27   $273.25   $273.30  
  7 purchase totals = $1,194.60       $1,304.6473   $1,304.64   $1,304.65   $1,304.70