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	$151.75	9.613%	$166.3377	$166.34	$166.35	$166.30
Purchase #2	$100.49	12.237%	$112.787	$112.79	$112.80	$112.80
Purchase #3	$211.63	10.521%	$233.8956	$233.90	$233.90	$233.90
Purchase #4	$137.27	11.757%	$153.4088	$153.41	$153.40	$153.40
Purchase #5	$100.50	3.736%	$104.2547	$104.25	$104.25	$104.30
Purchase #6	$54.61	13.610%	$62.0424	$62.04	$62.05	$62.00
Purchase #7	$39.94	12.657%	$44.9952	$45.00	$45.00	$45.00
7 purchase totals =	$796.19		$877.7214	$877.73	$877.75	$877.70