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	$56.84	5.426%	$59.9241	$59.92	$59.90	$59.90
Purchase #2	$43.56	6.764%	$46.5064	$46.51	$46.50	$46.50
Purchase #3	$136.63	9.392%	$149.4623	$149.46	$149.45	$149.50
Purchase #4	$91.36	9.142%	$99.7121	$99.71	$99.70	$99.70
Purchase #5	$171.25	11.650%	$191.2006	$191.20	$191.20	$191.20
Purchase #6	$34.80	13.540%	$39.5119	$39.51	$39.50	$39.50
Purchase #7	$127.70	5.392%	$134.5856	$134.59	$134.60	$134.60
7 purchase totals =	$662.14		$720.9030	$720.90	$720.85	$720.90