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	$66.72	9.379%	$72.9777	$72.98	$73.00	$73.00
Purchase #2	$46.98	8.411%	$50.9315	$50.93	$50.95	$50.90
Purchase #3	$23.64	12.342%	$26.5576	$26.56	$26.55	$26.60
Purchase #4	$134.58	3.848%	$139.7586	$139.76	$139.75	$139.80
Purchase #5	$151.89	12.625%	$171.0661	$171.07	$171.05	$171.10
Purchase #6	$177.35	4.763%	$185.7972	$185.80	$185.80	$185.80
Purchase #7	$35.76	5.633%	$37.7744	$37.77	$37.75	$37.80
7 purchase totals =	$636.92		$684.8631	$684.87	$684.85	$685.00