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	$11.74	9.573%	$12.8639	$12.86	$12.85	$12.90
Purchase #2	$100.60	3.438%	$104.0586	$104.06	$104.05	$104.10
Purchase #3	$176.64	11.197%	$196.4184	$196.42	$196.40	$196.40
Purchase #4	$141.26	6.440%	$150.3571	$150.36	$150.35	$150.40
Purchase #5	$166.87	8.145%	$180.4616	$180.46	$180.45	$180.50
Purchase #6	$93.40	7.727%	$100.617	$100.62	$100.60	$100.60
Purchase #7	$204.96	11.251%	$228.02	$228.02	$228.00	$228.00
7 purchase totals =	$895.47		$972.7966	$972.80	$972.70	$972.90