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	$138.56	7.305%	$148.6818	$148.68	$148.70	$148.70
Purchase #2	$182.65	11.201%	$203.1086	$203.11	$203.10	$203.10
Purchase #3	$172.92	6.291%	$183.7984	$183.80	$183.80	$183.80
Purchase #4	$118.56	7.626%	$127.6014	$127.60	$127.60	$127.60
Purchase #5	$153.27	7.236%	$164.3606	$164.36	$164.35	$164.40
Purchase #6	$158.54	11.224%	$176.3345	$176.33	$176.35	$176.30
Purchase #7	$52.45	13.242%	$59.3954	$59.40	$59.40	$59.40
7 purchase totals =	$976.95		$1,063.2807	$1,063.28	$1,063.30	$1,063.30