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	$89.85	9.622%	$98.4954	$98.50	$98.50	$98.50
Purchase #2	$28.86	5.324%	$30.3965	$30.40	$30.40	$30.40
Purchase #3	$198.49	12.661%	$223.6208	$223.62	$223.60	$223.60
Purchase #4	$88.64	12.803%	$99.9886	$99.99	$100.00	$100.00
Purchase #5	$144.85	11.526%	$161.5454	$161.55	$161.55	$161.50
Purchase #6	$49.91	4.240%	$52.0262	$52.03	$52.05	$52.00
Purchase #7	$134.57	13.529%	$152.776	$152.78	$152.80	$152.80
7 purchase totals =	$735.17		$818.8489	$818.87	$818.90	$818.80