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	$211.64	12.696%	$238.5098	$238.51	$238.50	$238.50
Purchase #2	$128.82	13.593%	$146.3305	$146.33	$146.35	$146.30
Purchase #3	$10.73	12.824%	$12.106	$12.11	$12.10	$12.10
Purchase #4	$218.30	5.769%	$230.8937	$230.89	$230.90	$230.90
Purchase #5	$220.74	4.570%	$230.8278	$230.83	$230.85	$230.80
Purchase #6	$150.57	11.501%	$167.8871	$167.89	$167.90	$167.90
Purchase #7	$152.72	6.455%	$162.5781	$162.58	$162.60	$162.60
7 purchase totals =	$1,093.52		$1,189.1330	$1,189.14	$1,189.20	$1,189.10