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	$215.76	7.362%	$231.6443	$231.64	$231.65	$231.60
Purchase #2	$115.28	11.222%	$128.2167	$128.22	$128.20	$128.20
Purchase #3	$78.98	9.533%	$86.5092	$86.51	$86.50	$86.50
Purchase #4	$10.38	13.386%	$11.7695	$11.77	$11.75	$11.80
Purchase #5	$99.98	11.467%	$111.4447	$111.44	$111.45	$111.40
Purchase #6	$122.77	4.737%	$128.5856	$128.59	$128.60	$128.60
Purchase #7	$167.26	8.106%	$180.8181	$180.82	$180.80	$180.80
7 purchase totals =	$810.41		$878.9881	$878.99	$878.95	$878.90