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	$54.96	8.773%	$59.7816	$59.78	$59.80	$59.80
Purchase #2	$59.54	11.737%	$66.5282	$66.53	$66.55	$66.50
Purchase #3	$200.33	9.371%	$219.1029	$219.10	$219.10	$219.10
Purchase #4	$147.35	11.178%	$163.8208	$163.82	$163.80	$163.80
Purchase #5	$219.55	10.245%	$242.0429	$242.04	$242.05	$242.00
Purchase #6	$37.38	13.673%	$42.491	$42.49	$42.50	$42.50
Purchase #7	$51.31	10.672%	$56.7858	$56.79	$56.80	$56.80
7 purchase totals =	$770.42		$850.5532	$850.55	$850.60	$850.50