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	$136.92	10.652%	$151.5047	$151.50	$151.50	$151.50
Purchase #2	$153.61	7.614%	$165.3059	$165.31	$165.30	$165.30
Purchase #3	$144.56	3.773%	$150.0142	$150.01	$150.00	$150.00
Purchase #4	$248.30	12.506%	$279.3524	$279.35	$279.35	$279.40
Purchase #5	$247.55	8.456%	$268.4828	$268.48	$268.50	$268.50
Purchase #6	$59.82	10.183%	$65.9115	$65.91	$65.90	$65.90
Purchase #7	$132.70	4.554%	$138.7432	$138.74	$138.75	$138.70
7 purchase totals =	$1,123.46		$1,219.3147	$1,219.30	$1,219.30	$1,219.30