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	$28.46	3.348%	$29.4128	$29.41	$29.40	$29.40
Purchase #2	$133.80	8.278%	$144.876	$144.88	$144.90	$144.90
Purchase #3	$115.72	12.693%	$130.4083	$130.41	$130.40	$130.40
Purchase #4	$225.63	5.551%	$238.1547	$238.15	$238.15	$238.20
Purchase #5	$150.80	9.517%	$165.1516	$165.15	$165.15	$165.20
Purchase #6	$44.40	13.526%	$50.4055	$50.41	$50.40	$50.40
Purchase #7	$244.69	11.204%	$272.1051	$272.11	$272.10	$272.10
7 purchase totals =	$943.50		$1,030.5140	$1,030.52	$1,030.50	$1,030.60