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	$189.70	13.595%	$215.4897	$215.49	$215.50	$215.50
Purchase #2	$128.27	13.548%	$145.648	$145.65	$145.65	$145.60
Purchase #3	$70.45	11.122%	$78.2854	$78.29	$78.30	$78.30
Purchase #4	$220.82	4.257%	$230.2203	$230.22	$230.20	$230.20
Purchase #5	$229.38	9.521%	$251.2193	$251.22	$251.20	$251.20
Purchase #6	$176.27	13.770%	$200.5424	$200.54	$200.55	$200.50
Purchase #7	$33.86	9.148%	$36.9575	$36.96	$36.95	$37.00
7 purchase totals =	$1,048.75		$1,158.3626	$1,158.37	$1,158.35	$1,158.30