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	$18.73	13.375%	$21.2351	$21.24	$21.25	$21.20
Purchase #2	$133.41	11.400%	$148.6187	$148.62	$148.60	$148.60
Purchase #3	$19.72	12.159%	$22.1178	$22.12	$22.10	$22.10
Purchase #4	$40.29	7.760%	$43.4165	$43.42	$43.40	$43.40
Purchase #5	$62.80	5.519%	$66.2659	$66.27	$66.25	$66.30
Purchase #6	$167.72	10.759%	$185.765	$185.77	$185.75	$185.80
Purchase #7	$220.87	5.660%	$233.3712	$233.37	$233.35	$233.40
7 purchase totals =	$663.54		$720.7902	$720.81	$720.70	$720.80