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	$121.51	8.549%	$131.8979	$131.90	$131.90	$131.90
Purchase #2	$125.49	4.689%	$131.3742	$131.37	$131.35	$131.40
Purchase #3	$38.52	10.202%	$42.4498	$42.45	$42.45	$42.40
Purchase #4	$9.47	13.414%	$10.7403	$10.74	$10.75	$10.70
Purchase #5	$209.98	9.152%	$229.1974	$229.20	$229.20	$229.20
Purchase #6	$245.59	13.318%	$278.2977	$278.30	$278.30	$278.30
Purchase #7	$79.28	9.233%	$86.5999	$86.60	$86.60	$86.60
7 purchase totals =	$829.84		$910.5572	$910.56	$910.55	$910.50