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	$26.41	11.562%	$29.4635	$29.46	$29.45	$29.50
Purchase #2	$133.71	13.585%	$151.8745	$151.87	$151.85	$151.90
Purchase #3	$185.64	3.603%	$192.3286	$192.33	$192.35	$192.30
Purchase #4	$58.55	6.780%	$62.5197	$62.52	$62.50	$62.50
Purchase #5	$132.76	4.853%	$139.2028	$139.20	$139.20	$139.20
Purchase #6	$244.90	13.630%	$278.2799	$278.28	$278.30	$278.30
Purchase #7	$116.46	10.386%	$128.5555	$128.56	$128.55	$128.60
7 purchase totals =	$898.43		$982.2245	$982.22	$982.20	$982.30