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	$100.55	4.805%	$105.3814	$105.38	$105.40	$105.40
Purchase #2	$80.43	3.737%	$83.4357	$83.44	$83.45	$83.40
Purchase #3	$119.73	6.314%	$127.2898	$127.29	$127.30	$127.30
Purchase #4	$214.92	7.104%	$230.1879	$230.19	$230.20	$230.20
Purchase #5	$129.72	12.637%	$146.1127	$146.11	$146.10	$146.10
Purchase #6	$127.90	4.381%	$133.5033	$133.50	$133.50	$133.50
Purchase #7	$90.29	7.335%	$96.9128	$96.91	$96.90	$96.90
7 purchase totals =	$863.54		$922.8236	$922.82	$922.85	$922.80