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	$50.38	13.236%	$57.0483	$57.05	$57.05	$57.00
Purchase #2	$70.73	10.173%	$77.9254	$77.93	$77.95	$77.90
Purchase #3	$145.87	7.381%	$156.6367	$156.64	$156.65	$156.60
Purchase #4	$35.63	10.847%	$39.4948	$39.49	$39.50	$39.50
Purchase #5	$111.59	10.367%	$123.1585	$123.16	$123.15	$123.20
Purchase #6	$92.99	8.251%	$100.6626	$100.66	$100.65	$100.70
Purchase #7	$101.54	6.734%	$108.3777	$108.38	$108.40	$108.40
7 purchase totals =	$608.73		$663.3040	$663.31	$663.35	$663.30