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	$17.34	6.793%	$18.5179	$18.52	$18.50	$18.50
Purchase #2	$75.26	5.467%	$79.3745	$79.37	$79.35	$79.40
Purchase #3	$99.88	10.526%	$110.3934	$110.39	$110.40	$110.40
Purchase #4	$96.97	8.663%	$105.3705	$105.37	$105.35	$105.40
Purchase #5	$102.43	9.183%	$111.8361	$111.84	$111.85	$111.80
Purchase #6	$12.51	7.750%	$13.4795	$13.48	$13.50	$13.50
Purchase #7	$54.72	13.861%	$62.3047	$62.30	$62.30	$62.30
7 purchase totals =	$459.11		$501.2766	$501.27	$501.25	$501.30