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	$37.87	11.721%	$42.3087	$42.31	$42.30	$42.30
Purchase #2	$232.69	8.189%	$251.745	$251.75	$251.75	$251.70
Purchase #3	$33.87	3.486%	$35.0507	$35.05	$35.05	$35.10
Purchase #4	$116.82	9.120%	$127.474	$127.47	$127.45	$127.50
Purchase #5	$223.69	13.181%	$253.1746	$253.17	$253.15	$253.20
Purchase #6	$228.48	11.467%	$254.6798	$254.68	$254.70	$254.70
Purchase #7	$140.30	11.226%	$156.0501	$156.05	$156.05	$156.10
7 purchase totals =	$1,013.72		$1,120.4829	$1,120.48	$1,120.45	$1,120.60