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	$45.97	12.848%	$51.8762	$51.88	$51.90	$51.90
Purchase #2	$235.33	3.107%	$242.6417	$242.64	$242.65	$242.60
Purchase #3	$130.50	13.871%	$148.6017	$148.60	$148.60	$148.60
Purchase #4	$6.76	11.761%	$7.555	$7.56	$7.55	$7.60
Purchase #5	$65.56	10.489%	$72.4366	$72.44	$72.45	$72.40
Purchase #6	$169.82	6.548%	$180.9398	$180.94	$180.95	$180.90
Purchase #7	$224.61	13.861%	$255.7432	$255.74	$255.75	$255.70
7 purchase totals =	$878.55		$959.7942	$959.80	$959.85	$959.70