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	$27.39	10.238%	$30.1942	$30.19	$30.20	$30.20
Purchase #2	$76.70	11.728%	$85.6954	$85.70	$85.70	$85.70
Purchase #3	$136.25	10.539%	$150.6094	$150.61	$150.60	$150.60
Purchase #4	$233.30	6.780%	$249.1177	$249.12	$249.10	$249.10
Purchase #5	$102.46	8.445%	$111.1127	$111.11	$111.10	$111.10
Purchase #6	$65.98	9.838%	$72.4711	$72.47	$72.45	$72.50
Purchase #7	$111.92	13.383%	$126.8983	$126.90	$126.90	$126.90
7 purchase totals =	$754.00		$826.0988	$826.10	$826.05	$826.10