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	$64.50	4.381%	$67.3257	$67.33	$67.35	$67.30
Purchase #2	$72.86	8.819%	$79.2855	$79.29	$79.30	$79.30
Purchase #3	$122.50	5.181%	$128.8467	$128.85	$128.85	$128.80
Purchase #4	$58.32	3.647%	$60.4469	$60.45	$60.45	$60.40
Purchase #5	$151.73	13.505%	$172.2211	$172.22	$172.20	$172.20
Purchase #6	$44.92	7.783%	$48.4161	$48.42	$48.40	$48.40
Purchase #7	$108.72	7.539%	$116.9164	$116.92	$116.90	$116.90
7 purchase totals =	$623.55		$673.4584	$673.48	$673.45	$673.30