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	$154.81	11.462%	$172.5543	$172.55	$172.55	$172.60
Purchase #2	$163.71	13.722%	$186.1743	$186.17	$186.15	$186.20
Purchase #3	$30.82	8.266%	$33.3676	$33.37	$33.35	$33.40
Purchase #4	$204.60	3.696%	$212.162	$212.16	$212.15	$212.20
Purchase #5	$94.37	11.705%	$105.416	$105.42	$105.40	$105.40
Purchase #6	$160.56	4.669%	$168.0565	$168.06	$168.05	$168.10
Purchase #7	$31.25	11.306%	$34.7831	$34.78	$34.80	$34.80
7 purchase totals =	$840.12		$912.5138	$912.51	$912.45	$912.70