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	$231.94	10.374%	$256.0015	$256.00	$256.00	$256.00
Purchase #2	$105.60	3.742%	$109.5516	$109.55	$109.55	$109.60
Purchase #3	$104.42	4.691%	$109.3183	$109.32	$109.30	$109.30
Purchase #4	$53.75	7.690%	$57.8834	$57.88	$57.90	$57.90
Purchase #5	$58.64	6.317%	$62.3443	$62.34	$62.35	$62.30
Purchase #6	$29.61	9.300%	$32.3637	$32.36	$32.35	$32.40
Purchase #7	$66.35	12.748%	$74.8083	$74.81	$74.80	$74.80
7 purchase totals =	$650.31		$702.2711	$702.26	$702.25	$702.30