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	$170.43	11.822%	$190.5782	$190.58	$190.60	$190.60
Purchase #2	$50.49	10.443%	$55.7627	$55.76	$55.75	$55.80
Purchase #3	$159.95	9.578%	$175.27	$175.27	$175.25	$175.30
Purchase #4	$117.73	4.841%	$123.4293	$123.43	$123.45	$123.40
Purchase #5	$209.68	9.824%	$230.279	$230.28	$230.30	$230.30
Purchase #6	$188.94	6.173%	$200.6033	$200.60	$200.60	$200.60
Purchase #7	$210.60	6.223%	$223.7056	$223.71	$223.70	$223.70
7 purchase totals =	$1,107.82		$1,199.6281	$1,199.63	$1,199.65	$1,199.70