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	$111.71	9.346%	$122.1504	$122.15	$122.15	$122.20
Purchase #2	$250.58	13.652%	$284.7892	$284.79	$284.80	$284.80
Purchase #3	$75.64	3.265%	$78.1096	$78.11	$78.10	$78.10
Purchase #4	$37.59	13.761%	$42.7628	$42.76	$42.75	$42.80
Purchase #5	$120.93	6.331%	$128.5861	$128.59	$128.60	$128.60
Purchase #6	$27.95	6.344%	$29.7231	$29.72	$29.70	$29.70
Purchase #7	$29.98	9.275%	$32.7606	$32.76	$32.75	$32.80
7 purchase totals =	$654.38		$718.8818	$718.88	$718.85	$719.00