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	$122.29	4.695%	$128.0315	$128.03	$128.05	$128.00
Purchase #2	$246.73	5.342%	$259.9103	$259.91	$259.90	$259.90
Purchase #3	$146.70	3.246%	$151.4619	$151.46	$151.45	$151.50
Purchase #4	$74.87	5.145%	$78.7221	$78.72	$78.70	$78.70
Purchase #5	$231.43	4.250%	$241.2658	$241.27	$241.25	$241.30
Purchase #6	$65.90	6.436%	$70.1413	$70.14	$70.15	$70.10
Purchase #7	$169.62	5.416%	$178.8066	$178.81	$178.80	$178.80
7 purchase totals =	$1,057.54		$1,108.3395	$1,108.34	$1,108.30	$1,108.30