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	$10.88	11.189%	$12.0974	$12.10	$12.10	$12.10
Purchase #2	$223.74	9.239%	$244.4113	$244.41	$244.40	$244.40
Purchase #3	$184.38	7.870%	$198.8907	$198.89	$198.90	$198.90
Purchase #4	$74.31	5.426%	$78.3421	$78.34	$78.35	$78.30
Purchase #5	$71.94	7.137%	$77.0744	$77.07	$77.05	$77.10
Purchase #6	$156.50	8.769%	$170.2235	$170.22	$170.20	$170.20
Purchase #7	$200.31	10.719%	$221.7812	$221.78	$221.80	$221.80
7 purchase totals =	$922.06		$1,002.8206	$1,002.81	$1,002.80	$1,002.80