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	$119.86	3.693%	$124.2864	$124.29	$124.30	$124.30
Purchase #2	$105.92	10.219%	$116.744	$116.74	$116.75	$116.70
Purchase #3	$41.53	11.536%	$46.3209	$46.32	$46.30	$46.30
Purchase #4	$59.99	9.204%	$65.5115	$65.51	$65.50	$65.50
Purchase #5	$146.32	10.778%	$162.0904	$162.09	$162.10	$162.10
Purchase #6	$114.93	7.473%	$123.5187	$123.52	$123.50	$123.50
Purchase #7	$174.88	13.248%	$198.0481	$198.05	$198.05	$198.00
7 purchase totals =	$763.43		$836.5200	$836.52	$836.50	$836.40