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	$179.32	5.105%	$188.4743	$188.47	$188.45	$188.50
Purchase #2	$222.32	3.676%	$230.4925	$230.49	$230.50	$230.50
Purchase #3	$133.52	4.646%	$139.7233	$139.72	$139.70	$139.70
Purchase #4	$104.60	6.180%	$111.0643	$111.06	$111.05	$111.10
Purchase #5	$233.44	7.296%	$250.4718	$250.47	$250.45	$250.50
Purchase #6	$217.98	5.287%	$229.5046	$229.50	$229.50	$229.50
Purchase #7	$57.84	13.788%	$65.815	$65.82	$65.80	$65.80
7 purchase totals =	$1,149.02		$1,215.5458	$1,215.53	$1,215.45	$1,215.60