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	$75.34	4.510%	$78.7378	$78.74	$78.75	$78.70
Purchase #2	$244.93	5.323%	$257.9676	$257.97	$257.95	$258.00
Purchase #3	$109.33	8.452%	$118.5706	$118.57	$118.55	$118.60
Purchase #4	$58.93	13.339%	$66.7907	$66.79	$66.80	$66.80
Purchase #5	$122.72	13.604%	$139.4148	$139.41	$139.40	$139.40
Purchase #6	$74.35	12.802%	$83.8683	$83.87	$83.85	$83.90
Purchase #7	$54.95	8.429%	$59.5817	$59.58	$59.60	$59.60
7 purchase totals =	$740.55		$804.9315	$804.93	$804.90	$805.00