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	$48.68	9.724%	$53.4136	$53.41	$53.40	$53.40
Purchase #2	$56.83	5.435%	$59.9187	$59.92	$59.90	$59.90
Purchase #3	$85.94	8.501%	$93.2458	$93.25	$93.25	$93.20
Purchase #4	$44.53	13.261%	$50.4351	$50.44	$50.45	$50.40
Purchase #5	$89.41	7.215%	$95.8609	$95.86	$95.85	$95.90
Purchase #6	$9.82	13.309%	$11.1269	$11.13	$11.15	$11.10
Purchase #7	$128.45	12.739%	$144.8132	$144.81	$144.80	$144.80
7 purchase totals =	$463.66		$508.8142	$508.82	$508.80	$508.70