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	$161.59	3.500%	$167.2457	$167.25	$167.25	$167.20
Purchase #2	$141.86	6.642%	$151.2823	$151.28	$151.30	$151.30
Purchase #3	$185.58	11.661%	$207.2205	$207.22	$207.20	$207.20
Purchase #4	$55.87	4.318%	$58.2825	$58.28	$58.30	$58.30
Purchase #5	$73.89	13.219%	$83.6575	$83.66	$83.65	$83.70
Purchase #6	$132.78	5.757%	$140.4241	$140.42	$140.40	$140.40
Purchase #7	$82.55	9.495%	$90.3881	$90.39	$90.40	$90.40
7 purchase totals =	$834.12		$898.5007	$898.50	$898.50	$898.50