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	$31.40	9.484%	$34.378	$34.38	$34.40	$34.40
Purchase #2	$20.91	9.350%	$22.8651	$22.87	$22.85	$22.90
Purchase #3	$53.29	7.738%	$57.4136	$57.41	$57.40	$57.40
Purchase #4	$132.52	13.547%	$150.4725	$150.47	$150.45	$150.50
Purchase #5	$31.91	11.551%	$35.5959	$35.60	$35.60	$35.60
Purchase #6	$211.83	9.713%	$232.405	$232.41	$232.40	$232.40
Purchase #7	$121.89	10.456%	$134.6348	$134.63	$134.65	$134.60
7 purchase totals =	$603.75		$667.7649	$667.77	$667.75	$667.80