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	$231.69	6.399%	$246.5158	$246.52	$246.50	$246.50
Purchase #2	$155.89	10.818%	$172.7542	$172.75	$172.75	$172.80
Purchase #3	$70.76	9.861%	$77.7376	$77.74	$77.75	$77.70
Purchase #4	$82.45	10.456%	$91.071	$91.07	$91.05	$91.10
Purchase #5	$237.82	9.261%	$259.8445	$259.84	$259.85	$259.80
Purchase #6	$143.83	13.130%	$162.7149	$162.71	$162.70	$162.70
Purchase #7	$179.28	11.473%	$199.8488	$199.85	$199.85	$199.80
7 purchase totals =	$1,101.72		$1,210.4868	$1,210.48	$1,210.45	$1,210.40