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	$99.53	10.449%	$109.9299	$109.93	$109.95	$109.90
Purchase #2	$124.26	5.226%	$130.7538	$130.75	$130.75	$130.80
Purchase #3	$33.77	10.683%	$37.3776	$37.38	$37.40	$37.40
Purchase #4	$99.38	12.527%	$111.8293	$111.83	$111.85	$111.80
Purchase #5	$205.55	5.397%	$216.6435	$216.64	$216.65	$216.60
Purchase #6	$53.69	12.202%	$60.2413	$60.24	$60.25	$60.20
Purchase #7	$49.61	8.710%	$53.931	$53.93	$53.95	$53.90
7 purchase totals =	$665.79		$720.7064	$720.70	$720.80	$720.60