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	$78.51	13.583%	$89.174	$89.17	$89.15	$89.20
Purchase #2	$130.59	3.595%	$135.2847	$135.28	$135.30	$135.30
Purchase #3	$93.71	11.818%	$104.7846	$104.78	$104.80	$104.80
Purchase #4	$83.52	8.178%	$90.3503	$90.35	$90.35	$90.40
Purchase #5	$220.91	12.846%	$249.2881	$249.29	$249.30	$249.30
Purchase #6	$92.69	7.862%	$99.9773	$99.98	$100.00	$100.00
Purchase #7	$72.80	3.365%	$75.2497	$75.25	$75.25	$75.20
7 purchase totals =	$772.73		$844.1087	$844.10	$844.15	$844.20