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	$27.82	13.792%	$31.6569	$31.66	$31.65	$31.70
Purchase #2	$139.59	8.642%	$151.6534	$151.65	$151.65	$151.70
Purchase #3	$103.77	4.258%	$108.1885	$108.19	$108.20	$108.20
Purchase #4	$18.54	12.683%	$20.8914	$20.89	$20.90	$20.90
Purchase #5	$107.27	3.673%	$111.21	$111.21	$111.20	$111.20
Purchase #6	$238.65	9.397%	$261.0759	$261.08	$261.10	$261.10
Purchase #7	$190.88	13.394%	$216.4465	$216.45	$216.45	$216.40
7 purchase totals =	$826.52		$901.1226	$901.13	$901.15	$901.20