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	$178.40	6.728%	$190.4028	$190.40	$190.40	$190.40
Purchase #2	$238.32	8.680%	$259.0062	$259.01	$259.00	$259.00
Purchase #3	$240.77	13.325%	$272.8526	$272.85	$272.85	$272.90
Purchase #4	$183.96	6.798%	$196.4656	$196.47	$196.45	$196.50
Purchase #5	$123.31	5.700%	$130.3387	$130.34	$130.35	$130.30
Purchase #6	$223.51	7.666%	$240.6443	$240.64	$240.65	$240.60
Purchase #7	$145.90	5.366%	$153.729	$153.73	$153.75	$153.70
7 purchase totals =	$1,334.17		$1,443.4392	$1,443.44	$1,443.45	$1,443.40