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	$16.78	10.298%	$18.508	$18.51	$18.50	$18.50
Purchase #2	$16.88	13.792%	$19.2081	$19.21	$19.20	$19.20
Purchase #3	$17.65	5.448%	$18.6116	$18.61	$18.60	$18.60
Purchase #4	$218.69	11.639%	$244.1433	$244.14	$244.15	$244.10
Purchase #5	$99.77	6.347%	$106.1024	$106.10	$106.10	$106.10
Purchase #6	$198.83	12.462%	$223.6082	$223.61	$223.60	$223.60
Purchase #7	$22.79	11.162%	$25.3338	$25.33	$25.35	$25.30
7 purchase totals =	$591.39		$655.5154	$655.51	$655.50	$655.40