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	$16.37	10.462%	$18.0826	$18.08	$18.10	$18.10
Purchase #2	$152.45	13.108%	$172.4331	$172.43	$172.45	$172.40
Purchase #3	$90.62	10.510%	$100.1442	$100.14	$100.15	$100.10
Purchase #4	$71.81	9.568%	$78.6808	$78.68	$78.70	$78.70
Purchase #5	$238.42	13.306%	$270.1442	$270.14	$270.15	$270.10
Purchase #6	$143.50	13.263%	$162.5324	$162.53	$162.55	$162.50
Purchase #7	$94.78	4.721%	$99.2546	$99.25	$99.25	$99.30
7 purchase totals =	$807.95		$901.2719	$901.25	$901.35	$901.20