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	$72.50	9.820%	$79.6195	$79.62	$79.60	$79.60
Purchase #2	$152.38	11.501%	$169.9052	$169.91	$169.90	$169.90
Purchase #3	$78.47	7.128%	$84.0633	$84.06	$84.05	$84.10
Purchase #4	$211.38	5.163%	$222.2935	$222.29	$222.30	$222.30
Purchase #5	$172.82	13.653%	$196.4151	$196.42	$196.40	$196.40
Purchase #6	$241.26	6.797%	$257.6584	$257.66	$257.65	$257.70
Purchase #7	$211.26	10.542%	$233.531	$233.53	$233.55	$233.50
7 purchase totals =	$1,140.07		$1,243.4860	$1,243.49	$1,243.45	$1,243.50