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	$138.65	5.651%	$146.4851	$146.49	$146.50	$146.50
Purchase #2	$55.36	8.476%	$60.0523	$60.05	$60.05	$60.10
Purchase #3	$53.41	8.374%	$57.8826	$57.88	$57.90	$57.90
Purchase #4	$105.72	5.833%	$111.8866	$111.89	$111.90	$111.90
Purchase #5	$132.79	6.722%	$141.7161	$141.72	$141.70	$141.70
Purchase #6	$65.52	7.332%	$70.3239	$70.32	$70.30	$70.30
Purchase #7	$150.60	12.151%	$168.8994	$168.90	$168.90	$168.90
7 purchase totals =	$702.05		$757.2460	$757.25	$757.25	$757.30