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	$155.77	4.593%	$162.9245	$162.92	$162.90	$162.90
Purchase #2	$117.80	11.338%	$131.1562	$131.16	$131.15	$131.20
Purchase #3	$111.48	10.199%	$122.8498	$122.85	$122.85	$122.80
Purchase #4	$145.59	7.584%	$156.6315	$156.63	$156.65	$156.60
Purchase #5	$163.34	5.536%	$172.3825	$172.38	$172.40	$172.40
Purchase #6	$158.59	4.390%	$165.5521	$165.55	$165.55	$165.60
Purchase #7	$18.39	9.716%	$20.1768	$20.18	$20.20	$20.20
7 purchase totals =	$870.96		$931.6734	$931.67	$931.70	$931.70