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	$187.41	13.361%	$212.4499	$212.45	$212.45	$212.40
Purchase #2	$143.71	4.384%	$150.0102	$150.01	$150.00	$150.00
Purchase #3	$59.87	11.675%	$66.8598	$66.86	$66.85	$66.90
Purchase #4	$211.98	7.120%	$227.073	$227.07	$227.05	$227.10
Purchase #5	$35.78	13.545%	$40.6264	$40.63	$40.65	$40.60
Purchase #6	$41.49	9.866%	$45.5834	$45.58	$45.60	$45.60
Purchase #7	$14.88	9.555%	$16.3018	$16.30	$16.30	$16.30
7 purchase totals =	$695.12		$758.9045	$758.90	$758.90	$758.90