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	$140.79	3.189%	$145.2798	$145.28	$145.30	$145.30
Purchase #2	$18.26	13.452%	$20.7163	$20.72	$20.70	$20.70
Purchase #3	$85.92	4.267%	$89.5862	$89.59	$89.60	$89.60
Purchase #4	$115.52	4.261%	$120.4423	$120.44	$120.45	$120.40
Purchase #5	$5.82	4.858%	$6.1027	$6.10	$6.10	$6.10
Purchase #6	$77.35	10.561%	$85.5189	$85.52	$85.50	$85.50
Purchase #7	$154.50	3.242%	$159.5089	$159.51	$159.50	$159.50
7 purchase totals =	$598.16		$627.1551	$627.16	$627.15	$627.10