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	$11.48	3.107%	$11.8367	$11.84	$11.85	$11.80
Purchase #2	$212.69	3.103%	$219.2898	$219.29	$219.30	$219.30
Purchase #3	$107.27	4.374%	$111.962	$111.96	$111.95	$112.00
Purchase #4	$173.58	10.274%	$191.4136	$191.41	$191.40	$191.40
Purchase #5	$92.38	8.695%	$100.4124	$100.41	$100.40	$100.40
Purchase #6	$28.68	5.209%	$30.1739	$30.17	$30.15	$30.20
Purchase #7	$159.50	4.866%	$167.2613	$167.26	$167.25	$167.30
7 purchase totals =	$785.58		$832.3497	$832.34	$832.30	$832.40