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	$52.65	8.114%	$56.922	$56.92	$56.90	$56.90
Purchase #2	$116.29	13.300%	$131.7566	$131.76	$131.75	$131.80
Purchase #3	$141.90	12.261%	$159.2984	$159.30	$159.30	$159.30
Purchase #4	$54.35	9.476%	$59.5002	$59.50	$59.50	$59.50
Purchase #5	$69.37	11.844%	$77.5862	$77.59	$77.60	$77.60
Purchase #6	$115.90	3.142%	$119.5416	$119.54	$119.55	$119.50
Purchase #7	$91.61	11.562%	$102.2019	$102.20	$102.20	$102.20
7 purchase totals =	$642.07		$706.8069	$706.81	$706.80	$706.80