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	$79.64	12.493%	$89.5894	$89.59	$89.60	$89.60
Purchase #2	$140.49	13.872%	$159.9788	$159.98	$160.00	$160.00
Purchase #3	$102.28	7.478%	$109.9285	$109.93	$109.95	$109.90
Purchase #4	$142.70	11.384%	$158.945	$158.95	$158.95	$158.90
Purchase #5	$224.31	12.325%	$251.9562	$251.96	$251.95	$252.00
Purchase #6	$196.58	4.851%	$206.1161	$206.12	$206.10	$206.10
Purchase #7	$111.31	6.354%	$118.3826	$118.38	$118.40	$118.40
7 purchase totals =	$997.31		$1,094.8966	$1,094.91	$1,094.95	$1,094.90