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	$38.80	4.572%	$40.5739	$40.57	$40.55	$40.60
Purchase #2	$176.43	13.591%	$200.4086	$200.41	$200.40	$200.40
Purchase #3	$128.28	13.664%	$145.8082	$145.81	$145.80	$145.80
Purchase #4	$103.83	12.265%	$116.5647	$116.56	$116.55	$116.60
Purchase #5	$118.79	13.773%	$135.1509	$135.15	$135.15	$135.20
Purchase #6	$74.80	3.172%	$77.1727	$77.17	$77.15	$77.20
Purchase #7	$196.25	13.323%	$222.3964	$222.40	$222.40	$222.40
7 purchase totals =	$837.18		$938.0754	$938.07	$938.00	$938.20