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	$86.81	3.442%	$89.798	$89.80	$89.80	$89.80
Purchase #2	$203.44	5.508%	$214.6455	$214.65	$214.65	$214.60
Purchase #3	$212.44	4.824%	$222.6881	$222.69	$222.70	$222.70
Purchase #4	$37.90	7.178%	$40.6205	$40.62	$40.60	$40.60
Purchase #5	$221.38	9.288%	$241.9418	$241.94	$241.95	$241.90
Purchase #6	$48.72	5.251%	$51.2783	$51.28	$51.30	$51.30
Purchase #7	$11.73	13.725%	$13.3399	$13.34	$13.35	$13.30
7 purchase totals =	$822.42		$874.3121	$874.32	$874.35	$874.20