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	$18.52	7.427%	$19.8955	$19.90	$19.90	$19.90
Purchase #2	$78.65	5.472%	$82.9537	$82.95	$82.95	$83.00
Purchase #3	$68.59	11.279%	$76.3263	$76.33	$76.35	$76.30
Purchase #4	$157.75	9.170%	$172.2157	$172.22	$172.20	$172.20
Purchase #5	$218.49	10.123%	$240.6077	$240.61	$240.60	$240.60
Purchase #6	$113.78	7.297%	$122.0825	$122.08	$122.10	$122.10
Purchase #7	$87.76	4.242%	$91.4828	$91.48	$91.50	$91.50
7 purchase totals =	$743.54		$805.5642	$805.57	$805.60	$805.60