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	$235.82	13.157%	$266.8468	$266.85	$266.85	$266.80
Purchase #2	$214.46	11.284%	$238.6597	$238.66	$238.65	$238.70
Purchase #3	$63.61	6.457%	$67.7173	$67.72	$67.70	$67.70
Purchase #4	$211.28	10.392%	$233.2362	$233.24	$233.25	$233.20
Purchase #5	$64.90	11.438%	$72.3233	$72.32	$72.30	$72.30
Purchase #6	$210.79	3.487%	$218.1402	$218.14	$218.15	$218.10
Purchase #7	$99.92	9.711%	$109.6232	$109.62	$109.60	$109.60
7 purchase totals =	$1,100.78		$1,206.5467	$1,206.55	$1,206.50	$1,206.40