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	$90.76	9.157%	$99.0709	$99.07	$99.05	$99.10
Purchase #2	$192.29	13.643%	$218.5241	$218.52	$218.50	$218.50
Purchase #3	$85.64	11.439%	$95.4364	$95.44	$95.45	$95.40
Purchase #4	$50.87	4.110%	$52.9608	$52.96	$52.95	$53.00
Purchase #5	$164.76	4.751%	$172.5877	$172.59	$172.60	$172.60
Purchase #6	$96.44	7.314%	$103.4936	$103.49	$103.50	$103.50
Purchase #7	$83.69	6.405%	$89.0503	$89.05	$89.05	$89.10
7 purchase totals =	$764.45		$831.1238	$831.12	$831.10	$831.20