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	$243.30	6.597%	$259.3505	$259.35	$259.35	$259.40
Purchase #2	$84.70	7.153%	$90.7586	$90.76	$90.75	$90.80
Purchase #3	$70.96	5.577%	$74.9174	$74.92	$74.90	$74.90
Purchase #4	$212.46	7.635%	$228.6813	$228.68	$228.70	$228.70
Purchase #5	$78.65	13.477%	$89.2497	$89.25	$89.25	$89.20
Purchase #6	$86.45	10.846%	$95.8264	$95.83	$95.85	$95.80
Purchase #7	$121.71	6.364%	$129.4556	$129.46	$129.45	$129.50
7 purchase totals =	$898.23		$968.2395	$968.25	$968.25	$968.30