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	$18.37	6.107%	$19.4919	$19.49	$19.50	$19.50
Purchase #2	$131.40	12.471%	$147.7869	$147.79	$147.80	$147.80
Purchase #3	$144.37	7.714%	$155.5067	$155.51	$155.50	$155.50
Purchase #4	$90.61	9.801%	$99.4907	$99.49	$99.50	$99.50
Purchase #5	$15.30	12.304%	$17.1825	$17.18	$17.20	$17.20
Purchase #6	$137.66	4.159%	$143.3853	$143.39	$143.40	$143.40
Purchase #7	$171.65	5.752%	$181.5233	$181.52	$181.50	$181.50
7 purchase totals =	$709.36		$764.3673	$764.37	$764.40	$764.40