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	$6.29	9.231%	$6.8706	$6.87	$6.85	$6.90
Purchase #2	$122.88	13.845%	$139.8927	$139.89	$139.90	$139.90
Purchase #3	$122.75	13.726%	$139.5987	$139.60	$139.60	$139.60
Purchase #4	$37.57	9.725%	$41.2237	$41.22	$41.20	$41.20
Purchase #5	$165.88	3.393%	$171.5083	$171.51	$171.50	$171.50
Purchase #6	$113.25	4.445%	$118.284	$118.28	$118.30	$118.30
Purchase #7	$144.91	4.421%	$151.3165	$151.32	$151.30	$151.30
7 purchase totals =	$713.53		$768.6945	$768.69	$768.65	$768.70