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	$159.61	12.578%	$179.6857	$179.69	$179.70	$179.70
Purchase #2	$93.79	10.405%	$103.5488	$103.55	$103.55	$103.50
Purchase #3	$99.59	9.491%	$109.0421	$109.04	$109.05	$109.00
Purchase #4	$65.27	12.241%	$73.2597	$73.26	$73.25	$73.30
Purchase #5	$170.54	5.286%	$179.5547	$179.55	$179.55	$179.60
Purchase #6	$145.51	5.268%	$153.1755	$153.18	$153.20	$153.20
Purchase #7	$75.46	4.544%	$78.8889	$78.89	$78.90	$78.90
7 purchase totals =	$809.77		$877.1554	$877.16	$877.20	$877.20