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	$31.28	7.849%	$33.7352	$33.74	$33.75	$33.70
Purchase #2	$214.86	11.172%	$238.8642	$238.86	$238.85	$238.90
Purchase #3	$184.95	4.320%	$192.9398	$192.94	$192.95	$192.90
Purchase #4	$98.77	10.270%	$108.9137	$108.91	$108.90	$108.90
Purchase #5	$12.27	5.537%	$12.9494	$12.95	$12.95	$12.90
Purchase #6	$7.56	10.172%	$8.329	$8.33	$8.35	$8.30
Purchase #7	$186.46	7.503%	$200.4501	$200.45	$200.45	$200.50
7 purchase totals =	$736.15		$796.1814	$796.18	$796.20	$796.10