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	$194.81	12.381%	$218.9294	$218.93	$218.95	$218.90
Purchase #2	$52.30	10.453%	$57.7669	$57.77	$57.75	$57.80
Purchase #3	$94.41	10.418%	$104.2456	$104.25	$104.25	$104.20
Purchase #4	$132.75	13.243%	$150.3301	$150.33	$150.35	$150.30
Purchase #5	$246.67	3.167%	$254.482	$254.48	$254.50	$254.50
Purchase #6	$241.50	5.193%	$254.0411	$254.04	$254.05	$254.00
Purchase #7	$230.78	12.191%	$258.9144	$258.91	$258.90	$258.90
7 purchase totals =	$1,193.22		$1,298.7095	$1,298.71	$1,298.75	$1,298.60