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	$128.60	4.621%	$134.5426	$134.54	$134.55	$134.50
Purchase #2	$83.68	8.198%	$90.5401	$90.54	$90.55	$90.50
Purchase #3	$120.55	5.383%	$127.0392	$127.04	$127.05	$127.00
Purchase #4	$225.35	8.404%	$244.2884	$244.29	$244.30	$244.30
Purchase #5	$33.99	13.285%	$38.5056	$38.51	$38.50	$38.50
Purchase #6	$190.74	5.844%	$201.8868	$201.89	$201.90	$201.90
Purchase #7	$153.73	11.747%	$171.7887	$171.79	$171.80	$171.80
7 purchase totals =	$936.64		$1,008.5914	$1,008.60	$1,008.65	$1,008.50