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	$34.70	13.249%	$39.2974	$39.30	$39.30	$39.30
Purchase #2	$96.78	4.647%	$101.2774	$101.28	$101.30	$101.30
Purchase #3	$109.81	11.564%	$122.5084	$122.51	$122.50	$122.50
Purchase #4	$101.81	6.197%	$108.1192	$108.12	$108.10	$108.10
Purchase #5	$85.69	6.172%	$90.9788	$90.98	$91.00	$91.00
Purchase #6	$66.48	11.789%	$74.3173	$74.32	$74.30	$74.30
Purchase #7	$57.58	3.396%	$59.5354	$59.54	$59.55	$59.50
7 purchase totals =	$552.85		$596.0339	$596.05	$596.05	$596.00