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	$55.30	13.563%	$62.8003	$62.80	$62.80	$62.80
Purchase #2	$100.76	10.424%	$111.2632	$111.26	$111.25	$111.30
Purchase #3	$35.51	11.120%	$39.4587	$39.46	$39.45	$39.50
Purchase #4	$142.64	3.235%	$147.2544	$147.25	$147.25	$147.30
Purchase #5	$167.75	6.137%	$178.0448	$178.04	$178.05	$178.00
Purchase #6	$166.53	11.547%	$185.7592	$185.76	$185.75	$185.80
Purchase #7	$74.86	3.349%	$77.3671	$77.37	$77.35	$77.40
7 purchase totals =	$743.35		$801.9477	$801.94	$801.90	$802.10