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	$11.54	9.168%	$12.598	$12.60	$12.60	$12.60
Purchase #2	$96.55	7.447%	$103.7401	$103.74	$103.75	$103.70
Purchase #3	$22.49	13.665%	$25.5633	$25.56	$25.55	$25.60
Purchase #4	$61.98	12.139%	$69.5038	$69.50	$69.50	$69.50
Purchase #5	$56.65	9.867%	$62.2397	$62.24	$62.25	$62.20
Purchase #6	$75.80	8.777%	$82.453	$82.45	$82.45	$82.50
Purchase #7	$222.71	11.715%	$248.8005	$248.80	$248.80	$248.80
7 purchase totals =	$547.72		$604.8984	$604.89	$604.90	$604.90