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	$72.41	10.622%	$80.1014	$80.10	$80.10	$80.10
Purchase #2	$60.94	3.565%	$63.1125	$63.11	$63.10	$63.10
Purchase #3	$143.91	5.327%	$151.5761	$151.58	$151.60	$151.60
Purchase #4	$152.25	13.618%	$172.9834	$172.98	$173.00	$173.00
Purchase #5	$85.69	9.770%	$94.0619	$94.06	$94.05	$94.10
Purchase #6	$140.45	11.651%	$156.8138	$156.81	$156.80	$156.80
Purchase #7	$134.26	3.822%	$139.3914	$139.39	$139.40	$139.40
7 purchase totals =	$789.91		$858.0405	$858.03	$858.05	$858.10