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	$171.87	9.399%	$188.0241	$188.02	$188.00	$188.00
Purchase #2	$173.74	5.584%	$183.4416	$183.44	$183.45	$183.40
Purchase #3	$140.29	13.264%	$158.8981	$158.90	$158.90	$158.90
Purchase #4	$147.55	8.189%	$159.6329	$159.63	$159.65	$159.60
Purchase #5	$242.76	7.745%	$261.5618	$261.56	$261.55	$261.60
Purchase #6	$26.40	11.734%	$29.4978	$29.50	$29.50	$29.50
Purchase #7	$89.95	11.816%	$100.5785	$100.58	$100.60	$100.60
7 purchase totals =	$992.56		$1,081.6348	$1,081.63	$1,081.65	$1,081.60