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	$74.63	5.554%	$78.775	$78.78	$78.80	$78.80
Purchase #2	$218.69	5.193%	$230.0466	$230.05	$230.05	$230.00
Purchase #3	$25.56	11.340%	$28.4585	$28.46	$28.45	$28.50
Purchase #4	$233.99	12.632%	$263.5476	$263.55	$263.55	$263.50
Purchase #5	$113.80	13.317%	$128.9547	$128.95	$128.95	$129.00
Purchase #6	$106.77	4.382%	$111.4487	$111.45	$111.45	$111.40
Purchase #7	$138.99	3.700%	$144.1326	$144.13	$144.15	$144.10
7 purchase totals =	$912.43		$985.3637	$985.37	$985.40	$985.30