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	$53.40	8.418%	$57.8952	$57.90	$57.90	$57.90
Purchase #2	$181.72	4.397%	$189.7102	$189.71	$189.70	$189.70
Purchase #3	$103.40	8.782%	$112.4806	$112.48	$112.50	$112.50
Purchase #4	$214.77	9.841%	$235.9055	$235.91	$235.90	$235.90
Purchase #5	$49.76	4.866%	$52.1813	$52.18	$52.20	$52.20
Purchase #6	$58.55	5.697%	$61.8856	$61.89	$61.90	$61.90
Purchase #7	$26.85	7.340%	$28.8208	$28.82	$28.80	$28.80
7 purchase totals =	$688.45		$738.8792	$738.89	$738.90	$738.90