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	$16.42	12.314%	$18.442	$18.44	$18.45	$18.40
Purchase #2	$197.91	4.313%	$206.4459	$206.45	$206.45	$206.40
Purchase #3	$177.59	10.829%	$196.8212	$196.82	$196.80	$196.80
Purchase #4	$155.80	4.536%	$162.8671	$162.87	$162.85	$162.90
Purchase #5	$146.34	12.131%	$164.0925	$164.09	$164.10	$164.10
Purchase #6	$231.46	6.786%	$247.1669	$247.17	$247.15	$247.20
Purchase #7	$146.32	3.557%	$151.5246	$151.52	$151.50	$151.50
7 purchase totals =	$1,071.84		$1,147.3602	$1,147.36	$1,147.30	$1,147.30