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	$148.72	11.729%	$166.1634	$166.16	$166.15	$166.20
Purchase #2	$162.87	5.723%	$172.1911	$172.19	$172.20	$172.20
Purchase #3	$46.30	13.556%	$52.5764	$52.58	$52.60	$52.60
Purchase #4	$119.74	6.350%	$127.3435	$127.34	$127.35	$127.30
Purchase #5	$56.80	11.359%	$63.2519	$63.25	$63.25	$63.30
Purchase #6	$87.43	10.161%	$96.3138	$96.31	$96.30	$96.30
Purchase #7	$25.46	9.596%	$27.9031	$27.90	$27.90	$27.90
7 purchase totals =	$647.32		$705.7432	$705.73	$705.75	$705.80