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	$83.90	5.253%	$88.3073	$88.31	$88.30	$88.30
Purchase #2	$54.51	11.304%	$60.6718	$60.67	$60.65	$60.70
Purchase #3	$28.84	11.565%	$32.1753	$32.18	$32.20	$32.20
Purchase #4	$51.52	13.573%	$58.5128	$58.51	$58.50	$58.50
Purchase #5	$77.52	12.730%	$87.3883	$87.39	$87.40	$87.40
Purchase #6	$239.73	6.562%	$255.4611	$255.46	$255.45	$255.50
Purchase #7	$90.48	10.837%	$100.2853	$100.29	$100.30	$100.30
7 purchase totals =	$626.50		$682.8019	$682.81	$682.80	$682.90