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	$81.31	12.685%	$91.6242	$91.62	$91.60	$91.60
Purchase #2	$220.83	5.706%	$233.4306	$233.43	$233.45	$233.40
Purchase #3	$170.77	7.561%	$183.6819	$183.68	$183.70	$183.70
Purchase #4	$141.39	5.256%	$148.8215	$148.82	$148.80	$148.80
Purchase #5	$83.67	3.374%	$86.493	$86.49	$86.50	$86.50
Purchase #6	$136.61	7.155%	$146.3844	$146.38	$146.40	$146.40
Purchase #7	$9.88	12.755%	$11.1402	$11.14	$11.15	$11.10
7 purchase totals =	$844.46		$901.5758	$901.56	$901.60	$901.50