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	$106.89	4.590%	$111.7963	$111.80	$111.80	$111.80
Purchase #2	$119.75	12.362%	$134.5535	$134.55	$134.55	$134.60
Purchase #3	$156.67	13.493%	$177.8095	$177.81	$177.80	$177.80
Purchase #4	$173.34	6.105%	$183.9224	$183.92	$183.90	$183.90
Purchase #5	$33.37	12.159%	$37.4275	$37.43	$37.45	$37.40
Purchase #6	$85.79	4.252%	$89.4378	$89.44	$89.45	$89.40
Purchase #7	$139.48	6.113%	$148.0064	$148.01	$148.00	$148.00
7 purchase totals =	$815.29		$882.9534	$882.96	$882.95	$882.90