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	$204.38	6.578%	$217.8241	$217.82	$217.80	$217.80
Purchase #2	$70.38	13.191%	$79.6638	$79.66	$79.65	$79.70
Purchase #3	$228.49	12.233%	$256.4412	$256.44	$256.45	$256.40
Purchase #4	$33.64	6.385%	$35.7879	$35.79	$35.80	$35.80
Purchase #5	$25.70	8.261%	$27.8231	$27.82	$27.80	$27.80
Purchase #6	$6.31	13.458%	$7.1592	$7.16	$7.15	$7.20
Purchase #7	$185.60	6.115%	$196.9494	$196.95	$196.95	$196.90
7 purchase totals =	$754.50		$821.6487	$821.64	$821.60	$821.60