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	$84.48	6.369%	$89.8605	$89.86	$89.85	$89.90
Purchase #2	$59.39	11.303%	$66.1029	$66.10	$66.10	$66.10
Purchase #3	$212.25	13.709%	$241.3474	$241.35	$241.35	$241.30
Purchase #4	$139.80	13.523%	$158.7052	$158.71	$158.70	$158.70
Purchase #5	$132.73	11.690%	$148.2461	$148.25	$148.25	$148.20
Purchase #6	$144.81	10.647%	$160.2279	$160.23	$160.25	$160.20
Purchase #7	$114.51	13.317%	$129.7593	$129.76	$129.75	$129.80
7 purchase totals =	$887.97		$994.2493	$994.26	$994.25	$994.20