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	$48.29	13.736%	$54.9231	$54.92	$54.90	$54.90
Purchase #2	$100.89	12.695%	$113.698	$113.70	$113.70	$113.70
Purchase #3	$247.36	13.145%	$279.8755	$279.88	$279.90	$279.90
Purchase #4	$196.30	5.489%	$207.0749	$207.07	$207.05	$207.10
Purchase #5	$16.59	11.358%	$18.4743	$18.47	$18.45	$18.50
Purchase #6	$137.97	12.770%	$155.5888	$155.59	$155.60	$155.60
Purchase #7	$172.51	9.465%	$188.8381	$188.84	$188.85	$188.80
7 purchase totals =	$919.91		$1,018.4727	$1,018.47	$1,018.45	$1,018.50