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	$170.66	4.357%	$178.0957	$178.10	$178.10	$178.10
Purchase #2	$69.77	9.325%	$76.2761	$76.28	$76.30	$76.30
Purchase #3	$98.31	10.561%	$108.6925	$108.69	$108.70	$108.70
Purchase #4	$193.85	11.817%	$216.7573	$216.76	$216.75	$216.80
Purchase #5	$238.94	11.258%	$265.8399	$265.84	$265.85	$265.80
Purchase #6	$113.47	12.231%	$127.3485	$127.35	$127.35	$127.30
Purchase #7	$106.70	4.249%	$111.2337	$111.23	$111.25	$111.20
7 purchase totals =	$991.70		$1,084.2437	$1,084.25	$1,084.30	$1,084.20