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	$26.94	7.609%	$28.9899	$28.99	$29.00	$29.00
Purchase #2	$71.86	13.352%	$81.4547	$81.45	$81.45	$81.50
Purchase #3	$44.93	7.866%	$48.4642	$48.46	$48.45	$48.50
Purchase #4	$232.39	10.281%	$256.282	$256.28	$256.30	$256.30
Purchase #5	$57.78	3.606%	$59.8635	$59.86	$59.85	$59.90
Purchase #6	$83.50	12.682%	$94.0895	$94.09	$94.10	$94.10
Purchase #7	$28.92	7.732%	$31.1561	$31.16	$31.15	$31.20
7 purchase totals =	$546.32		$600.2999	$600.29	$600.30	$600.50