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	$54.89	3.525%	$56.8249	$56.82	$56.80	$56.80
Purchase #2	$240.89	7.518%	$259.0001	$259.00	$259.00	$259.00
Purchase #3	$146.37	3.617%	$151.6642	$151.66	$151.65	$151.70
Purchase #4	$54.99	7.720%	$59.2352	$59.24	$59.25	$59.20
Purchase #5	$102.51	7.668%	$110.3705	$110.37	$110.35	$110.40
Purchase #6	$154.52	11.193%	$171.8154	$171.82	$171.80	$171.80
Purchase #7	$50.89	8.713%	$55.324	$55.32	$55.30	$55.30
7 purchase totals =	$805.06		$864.2343	$864.23	$864.15	$864.20