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	$222.51	7.605%	$239.4319	$239.43	$239.45	$239.40
Purchase #2	$145.45	4.199%	$151.5574	$151.56	$151.55	$151.60
Purchase #3	$150.28	10.636%	$166.2638	$166.26	$166.25	$166.30
Purchase #4	$169.48	3.534%	$175.4694	$175.47	$175.45	$175.50
Purchase #5	$138.67	5.389%	$146.1429	$146.14	$146.15	$146.10
Purchase #6	$41.44	3.585%	$42.9256	$42.93	$42.95	$42.90
Purchase #7	$140.48	13.646%	$159.6499	$159.65	$159.65	$159.60
7 purchase totals =	$1,008.31		$1,081.4409	$1,081.44	$1,081.45	$1,081.40