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	$194.73	13.216%	$220.4655	$220.47	$220.45	$220.50
Purchase #2	$38.63	10.730%	$42.775	$42.78	$42.80	$42.80
Purchase #3	$6.38	3.649%	$6.6128	$6.61	$6.60	$6.60
Purchase #4	$133.36	7.306%	$143.1033	$143.10	$143.10	$143.10
Purchase #5	$73.80	13.475%	$83.7446	$83.74	$83.75	$83.70
Purchase #6	$67.31	6.614%	$71.7619	$71.76	$71.75	$71.80
Purchase #7	$180.57	8.549%	$196.0069	$196.01	$196.00	$196.00
7 purchase totals =	$694.78		$764.4700	$764.47	$764.45	$764.50