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	$240.83	5.810%	$254.8222	$254.82	$254.80	$254.80
Purchase #2	$193.98	6.637%	$206.8545	$206.85	$206.85	$206.90
Purchase #3	$53.32	6.685%	$56.8844	$56.88	$56.90	$56.90
Purchase #4	$172.38	7.576%	$185.4395	$185.44	$185.45	$185.40
Purchase #5	$47.79	10.358%	$52.7401	$52.74	$52.75	$52.70
Purchase #6	$37.64	13.192%	$42.6055	$42.61	$42.60	$42.60
Purchase #7	$74.71	3.753%	$77.5139	$77.51	$77.50	$77.50
7 purchase totals =	$820.65		$876.8601	$876.85	$876.85	$876.80