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	$43.61	5.289%	$45.9165	$45.92	$45.90	$45.90
Purchase #2	$26.85	5.442%	$28.3112	$28.31	$28.30	$28.30
Purchase #3	$99.28	6.139%	$105.3748	$105.37	$105.35	$105.40
Purchase #4	$50.76	9.295%	$55.4781	$55.48	$55.50	$55.50
Purchase #5	$6.91	11.201%	$7.684	$7.68	$7.70	$7.70
Purchase #6	$175.89	11.823%	$196.6855	$196.69	$196.70	$196.70
Purchase #7	$187.91	10.234%	$207.1407	$207.14	$207.15	$207.10
7 purchase totals =	$591.21		$646.5908	$646.59	$646.60	$646.60