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	$150.56	6.428%	$160.238	$160.24	$160.25	$160.20
Purchase #2	$167.82	11.141%	$186.5168	$186.52	$186.50	$186.50
Purchase #3	$37.78	6.452%	$40.2176	$40.22	$40.20	$40.20
Purchase #4	$138.34	7.655%	$148.9299	$148.93	$148.95	$148.90
Purchase #5	$105.90	7.542%	$113.887	$113.89	$113.90	$113.90
Purchase #6	$106.29	5.405%	$112.035	$112.04	$112.05	$112.00
Purchase #7	$123.93	4.350%	$129.321	$129.32	$129.30	$129.30
7 purchase totals =	$830.62		$891.1453	$891.16	$891.15	$891.00