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	$225.95	13.185%	$255.7415	$255.74	$255.75	$255.70
Purchase #2	$92.29	7.479%	$99.1924	$99.19	$99.20	$99.20
Purchase #3	$220.53	3.231%	$227.6553	$227.66	$227.65	$227.70
Purchase #4	$37.78	6.215%	$40.128	$40.13	$40.15	$40.10
Purchase #5	$12.66	7.352%	$13.5908	$13.59	$13.60	$13.60
Purchase #6	$128.34	13.312%	$145.4246	$145.42	$145.40	$145.40
Purchase #7	$155.61	9.688%	$170.6855	$170.69	$170.70	$170.70
7 purchase totals =	$873.16		$952.4181	$952.42	$952.45	$952.40