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	$128.55	11.813%	$143.7356	$143.74	$143.75	$143.70
Purchase #2	$13.86	4.496%	$14.4831	$14.48	$14.50	$14.50
Purchase #3	$123.98	11.587%	$138.3456	$138.35	$138.35	$138.30
Purchase #4	$172.82	7.374%	$185.5637	$185.56	$185.55	$185.60
Purchase #5	$24.75	10.744%	$27.4091	$27.41	$27.40	$27.40
Purchase #6	$38.76	10.581%	$42.8612	$42.86	$42.85	$42.90
Purchase #7	$36.56	9.329%	$39.9707	$39.97	$39.95	$40.00
7 purchase totals =	$539.28		$592.3690	$592.37	$592.35	$592.40