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	$27.45	6.770%	$29.3084	$29.31	$29.30	$29.30
Purchase #2	$57.61	11.320%	$64.1315	$64.13	$64.15	$64.10
Purchase #3	$17.76	13.421%	$20.1436	$20.14	$20.15	$20.10
Purchase #4	$80.37	3.444%	$83.1379	$83.14	$83.15	$83.10
Purchase #5	$129.96	12.535%	$146.2505	$146.25	$146.25	$146.30
Purchase #6	$229.31	10.680%	$253.8003	$253.80	$253.80	$253.80
Purchase #7	$17.76	4.863%	$18.6237	$18.62	$18.60	$18.60
7 purchase totals =	$560.22		$615.3959	$615.39	$615.40	$615.30