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	$248.88	11.713%	$278.0313	$278.03	$278.05	$278.00
Purchase #2	$222.45	8.666%	$241.7275	$241.73	$241.75	$241.70
Purchase #3	$148.72	10.349%	$164.111	$164.11	$164.10	$164.10
Purchase #4	$114.90	10.696%	$127.1897	$127.19	$127.20	$127.20
Purchase #5	$147.25	12.440%	$165.5679	$165.57	$165.55	$165.60
Purchase #6	$122.30	9.700%	$134.1631	$134.16	$134.15	$134.20
Purchase #7	$56.54	8.605%	$61.4053	$61.41	$61.40	$61.40
7 purchase totals =	$1,061.04		$1,172.1958	$1,172.20	$1,172.20	$1,172.20