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	$34.74	12.375%	$39.0391	$39.04	$39.05	$39.00
Purchase #2	$27.82	5.206%	$29.2683	$29.27	$29.25	$29.30
Purchase #3	$211.53	10.609%	$233.9712	$233.97	$233.95	$234.00
Purchase #4	$40.70	3.548%	$42.144	$42.14	$42.15	$42.10
Purchase #5	$7.32	6.490%	$7.7951	$7.80	$7.80	$7.80
Purchase #6	$34.43	7.826%	$37.1245	$37.12	$37.10	$37.10
Purchase #7	$39.83	9.761%	$43.7178	$43.72	$43.70	$43.70
7 purchase totals =	$396.37		$433.0600	$433.06	$433.00	$433.00