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	$134.56	9.158%	$146.883	$146.88	$146.90	$146.90
Purchase #2	$189.52	7.168%	$203.1048	$203.10	$203.10	$203.10
Purchase #3	$56.87	4.134%	$59.221	$59.22	$59.20	$59.20
Purchase #4	$10.78	12.379%	$12.1145	$12.11	$12.10	$12.10
Purchase #5	$242.45	13.441%	$275.0377	$275.04	$275.05	$275.00
Purchase #6	$52.88	13.151%	$59.8342	$59.83	$59.85	$59.80
Purchase #7	$238.49	3.399%	$246.5963	$246.60	$246.60	$246.60
7 purchase totals =	$925.55		$1,002.7915	$1,002.78	$1,002.80	$1,002.70