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	$235.70	12.385%	$264.8914	$264.89	$264.90	$264.90
Purchase #2	$112.26	10.868%	$124.4604	$124.46	$124.45	$124.50
Purchase #3	$92.93	13.841%	$105.7924	$105.79	$105.80	$105.80
Purchase #4	$40.57	7.119%	$43.4582	$43.46	$43.45	$43.50
Purchase #5	$21.49	6.252%	$22.8336	$22.83	$22.85	$22.80
Purchase #6	$112.70	13.304%	$127.6936	$127.69	$127.70	$127.70
Purchase #7	$48.40	3.602%	$50.1434	$50.14	$50.15	$50.10
7 purchase totals =	$664.05		$739.2730	$739.26	$739.30	$739.30