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	$211.49	12.587%	$238.1102	$238.11	$238.10	$238.10
Purchase #2	$182.66	10.683%	$202.1736	$202.17	$202.15	$202.20
Purchase #3	$113.67	8.718%	$123.5798	$123.58	$123.60	$123.60
Purchase #4	$42.52	7.464%	$45.6937	$45.69	$45.70	$45.70
Purchase #5	$129.61	11.179%	$144.0991	$144.10	$144.10	$144.10
Purchase #6	$13.54	6.837%	$14.4657	$14.47	$14.45	$14.50
Purchase #7	$35.87	4.833%	$37.6036	$37.60	$37.60	$37.60
7 purchase totals =	$729.36		$805.7257	$805.72	$805.70	$805.80