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	$214.75	6.395%	$228.4833	$228.48	$228.50	$228.50
Purchase #2	$41.42	3.488%	$42.8647	$42.86	$42.85	$42.90
Purchase #3	$163.33	6.832%	$174.4887	$174.49	$174.50	$174.50
Purchase #4	$85.28	5.505%	$89.9747	$89.97	$89.95	$90.00
Purchase #5	$72.70	11.210%	$80.8497	$80.85	$80.85	$80.80
Purchase #6	$19.84	11.622%	$22.1458	$22.15	$22.15	$22.10
Purchase #7	$40.52	4.289%	$42.2579	$42.26	$42.25	$42.30
7 purchase totals =	$637.84		$681.0648	$681.06	$681.05	$681.10