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	$41.83	9.223%	$45.688	$45.69	$45.70	$45.70
Purchase #2	$181.87	8.488%	$197.3071	$197.31	$197.30	$197.30
Purchase #3	$74.92	13.554%	$85.0747	$85.07	$85.05	$85.10
Purchase #4	$99.87	8.690%	$108.5487	$108.55	$108.55	$108.50
Purchase #5	$155.98	6.535%	$166.1733	$166.17	$166.15	$166.20
Purchase #6	$178.29	8.197%	$192.9044	$192.90	$192.90	$192.90
Purchase #7	$67.60	7.797%	$72.8708	$72.87	$72.85	$72.90
7 purchase totals =	$800.36		$868.5670	$868.56	$868.50	$868.60