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	$127.54	5.528%	$134.5904	$134.59	$134.60	$134.60
Purchase #2	$63.90	3.776%	$66.3129	$66.31	$66.30	$66.30
Purchase #3	$183.76	10.136%	$202.3859	$202.39	$202.40	$202.40
Purchase #4	$97.91	11.797%	$109.4604	$109.46	$109.45	$109.50
Purchase #5	$53.25	12.485%	$59.8983	$59.90	$59.90	$59.90
Purchase #6	$151.34	9.459%	$165.6553	$165.66	$165.65	$165.70
Purchase #7	$99.34	4.286%	$103.5977	$103.60	$103.60	$103.60
7 purchase totals =	$777.04		$841.9009	$841.91	$841.90	$842.00