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	$235.69	4.173%	$245.5253	$245.53	$245.55	$245.50
Purchase #2	$128.31	9.456%	$140.443	$140.44	$140.45	$140.40
Purchase #3	$63.54	12.510%	$71.4889	$71.49	$71.50	$71.50
Purchase #4	$58.93	5.845%	$62.3745	$62.37	$62.35	$62.40
Purchase #5	$239.58	5.453%	$252.6443	$252.64	$252.65	$252.60
Purchase #6	$161.77	9.584%	$177.274	$177.27	$177.25	$177.30
Purchase #7	$59.85	12.310%	$67.2175	$67.22	$67.20	$67.20
7 purchase totals =	$947.67		$1,016.9675	$1,016.96	$1,016.95	$1,016.90