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	$154.51	9.278%	$168.8454	$168.85	$168.85	$168.80
Purchase #2	$204.65	8.539%	$222.1251	$222.13	$222.15	$222.10
Purchase #3	$135.42	11.542%	$151.0502	$151.05	$151.05	$151.10
Purchase #4	$117.34	10.741%	$129.9435	$129.94	$129.95	$129.90
Purchase #5	$235.41	5.809%	$249.085	$249.09	$249.10	$249.10
Purchase #6	$34.85	13.338%	$39.4983	$39.50	$39.50	$39.50
Purchase #7	$167.66	7.712%	$180.5899	$180.59	$180.60	$180.60
7 purchase totals =	$1,049.84		$1,141.1374	$1,141.15	$1,141.20	$1,141.10