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	$44.31	13.502%	$50.2927	$50.29	$50.30	$50.30
Purchase #2	$18.53	10.666%	$20.5064	$20.51	$20.50	$20.50
Purchase #3	$196.25	5.648%	$207.3342	$207.33	$207.35	$207.30
Purchase #4	$226.75	12.181%	$254.3704	$254.37	$254.35	$254.40
Purchase #5	$85.76	4.389%	$89.524	$89.52	$89.50	$89.50
Purchase #6	$40.94	10.406%	$45.2002	$45.20	$45.20	$45.20
Purchase #7	$122.53	10.452%	$135.3368	$135.34	$135.35	$135.30
7 purchase totals =	$735.07		$802.5647	$802.56	$802.55	$802.50