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	$108.94	13.353%	$123.4868	$123.49	$123.50	$123.50
Purchase #2	$120.87	8.428%	$131.0569	$131.06	$131.05	$131.10
Purchase #3	$127.29	4.363%	$132.8437	$132.84	$132.85	$132.80
Purchase #4	$42.78	10.253%	$47.1662	$47.17	$47.15	$47.20
Purchase #5	$69.29	12.611%	$78.0282	$78.03	$78.05	$78.00
Purchase #6	$237.39	7.139%	$254.3373	$254.34	$254.35	$254.30
Purchase #7	$49.92	6.385%	$53.1074	$53.11	$53.10	$53.10
7 purchase totals =	$756.48		$820.0265	$820.04	$820.05	$820.00