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	$165.71	13.424%	$187.9549	$187.95	$187.95	$188.00
Purchase #2	$57.65	3.373%	$59.5945	$59.59	$59.60	$59.60
Purchase #3	$185.35	10.813%	$205.3919	$205.39	$205.40	$205.40
Purchase #4	$229.28	13.240%	$259.6367	$259.64	$259.65	$259.60
Purchase #5	$98.94	12.744%	$111.5489	$111.55	$111.55	$111.50
Purchase #6	$153.57	13.161%	$173.7813	$173.78	$173.80	$173.80
Purchase #7	$21.32	7.168%	$22.8482	$22.85	$22.85	$22.80
7 purchase totals =	$911.82		$1,020.7564	$1,020.75	$1,020.80	$1,020.70