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	$37.41	12.847%	$42.2161	$42.22	$42.20	$42.20
Purchase #2	$19.88	13.134%	$22.491	$22.49	$22.50	$22.50
Purchase #3	$18.66	8.638%	$20.2719	$20.27	$20.25	$20.30
Purchase #4	$97.73	12.463%	$109.9101	$109.91	$109.90	$109.90
Purchase #5	$95.63	4.497%	$99.9305	$99.93	$99.95	$99.90
Purchase #6	$173.57	6.346%	$184.5848	$184.58	$184.60	$184.60
Purchase #7	$227.90	7.466%	$244.915	$244.92	$244.90	$244.90
7 purchase totals =	$670.78		$724.3194	$724.32	$724.30	$724.30