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	$199.51	4.193%	$207.8755	$207.88	$207.90	$207.90
Purchase #2	$245.87	13.809%	$279.8222	$279.82	$279.80	$279.80
Purchase #3	$178.68	5.469%	$188.452	$188.45	$188.45	$188.50
Purchase #4	$215.38	7.307%	$231.1178	$231.12	$231.10	$231.10
Purchase #5	$77.35	7.194%	$82.9146	$82.91	$82.90	$82.90
Purchase #6	$54.98	13.491%	$62.3974	$62.40	$62.40	$62.40
Purchase #7	$200.60	11.179%	$223.0251	$223.03	$223.05	$223.00
7 purchase totals =	$1,172.37		$1,275.6046	$1,275.61	$1,275.60	$1,275.60