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	$222.31	12.284%	$249.6186	$249.62	$249.60	$249.60
Purchase #2	$43.91	12.548%	$49.4198	$49.42	$49.40	$49.40
Purchase #3	$210.78	9.248%	$230.2729	$230.27	$230.25	$230.30
Purchase #4	$78.65	13.597%	$89.344	$89.34	$89.35	$89.30
Purchase #5	$65.38	3.624%	$67.7494	$67.75	$67.75	$67.70
Purchase #6	$23.65	6.403%	$25.1643	$25.16	$25.15	$25.20
Purchase #7	$233.80	10.483%	$258.3093	$258.31	$258.30	$258.30
7 purchase totals =	$878.48		$969.8783	$969.87	$969.80	$969.80