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	$18.76	5.785%	$19.8453	$19.85	$19.85	$19.80
Purchase #2	$145.63	11.604%	$162.5289	$162.53	$162.55	$162.50
Purchase #3	$47.59	7.538%	$51.1773	$51.18	$51.20	$51.20
Purchase #4	$33.83	13.606%	$38.4329	$38.43	$38.45	$38.40
Purchase #5	$106.70	11.240%	$118.6931	$118.69	$118.70	$118.70
Purchase #6	$153.64	12.160%	$172.3226	$172.32	$172.30	$172.30
Purchase #7	$172.89	3.767%	$179.4028	$179.40	$179.40	$179.40
7 purchase totals =	$679.04		$742.4029	$742.40	$742.45	$742.30