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	$61.72	6.625%	$65.809	$65.81	$65.80	$65.80
Purchase #2	$122.78	13.370%	$139.1957	$139.20	$139.20	$139.20
Purchase #3	$114.67	11.278%	$127.6025	$127.60	$127.60	$127.60
Purchase #4	$107.48	12.141%	$120.5291	$120.53	$120.55	$120.50
Purchase #5	$70.46	9.623%	$77.2404	$77.24	$77.25	$77.20
Purchase #6	$196.30	7.342%	$210.7123	$210.71	$210.70	$210.70
Purchase #7	$124.84	11.509%	$139.2078	$139.21	$139.20	$139.20
7 purchase totals =	$798.25		$880.2968	$880.30	$880.30	$880.20