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	$27.88	12.567%	$31.3837	$31.38	$31.40	$31.40
Purchase #2	$48.98	13.466%	$55.5756	$55.58	$55.60	$55.60
Purchase #3	$115.28	10.223%	$127.0651	$127.07	$127.05	$127.10
Purchase #4	$34.79	13.563%	$39.5086	$39.51	$39.50	$39.50
Purchase #5	$95.72	8.420%	$103.7796	$103.78	$103.80	$103.80
Purchase #6	$220.83	12.416%	$248.2483	$248.25	$248.25	$248.20
Purchase #7	$88.41	9.350%	$96.6763	$96.68	$96.70	$96.70
7 purchase totals =	$631.89		$702.2372	$702.25	$702.30	$702.30