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	$234.61	5.772%	$248.1517	$248.15	$248.15	$248.20
Purchase #2	$240.54	6.369%	$255.86	$255.86	$255.85	$255.90
Purchase #3	$165.63	6.827%	$176.9376	$176.94	$176.95	$176.90
Purchase #4	$153.55	12.687%	$173.0309	$173.03	$173.05	$173.00
Purchase #5	$30.76	8.755%	$33.453	$33.45	$33.45	$33.50
Purchase #6	$49.93	12.524%	$56.1832	$56.18	$56.20	$56.20
Purchase #7	$175.80	11.356%	$195.7638	$195.76	$195.75	$195.80
7 purchase totals =	$1,050.82		$1,139.3802	$1,139.37	$1,139.40	$1,139.50