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	$170.57	4.698%	$178.5834	$178.58	$178.60	$178.60
Purchase #2	$15.87	10.524%	$17.5402	$17.54	$17.55	$17.50
Purchase #3	$9.61	10.521%	$10.6211	$10.62	$10.60	$10.60
Purchase #4	$53.57	6.143%	$56.8608	$56.86	$56.85	$56.90
Purchase #5	$168.60	4.250%	$175.7655	$175.77	$175.75	$175.80
Purchase #6	$26.28	8.658%	$28.5553	$28.56	$28.55	$28.60
Purchase #7	$82.59	13.260%	$93.5414	$93.54	$93.55	$93.50
7 purchase totals =	$527.09		$561.4677	$561.47	$561.45	$561.50