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	$83.72	7.773%	$90.2276	$90.23	$90.25	$90.20
Purchase #2	$70.87	11.344%	$78.9095	$78.91	$78.90	$78.90
Purchase #3	$175.79	6.261%	$186.7962	$186.80	$186.80	$186.80
Purchase #4	$237.62	8.266%	$257.2617	$257.26	$257.25	$257.30
Purchase #5	$247.60	12.344%	$278.1637	$278.16	$278.15	$278.20
Purchase #6	$112.83	12.429%	$126.8536	$126.85	$126.85	$126.90
Purchase #7	$97.35	3.563%	$100.8186	$100.82	$100.80	$100.80
7 purchase totals =	$1,025.78		$1,119.0309	$1,119.03	$1,119.00	$1,119.10