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	$8.60	11.124%	$9.5567	$9.56	$9.55	$9.60
Purchase #2	$28.49	10.258%	$31.4125	$31.41	$31.40	$31.40
Purchase #3	$151.78	7.616%	$163.3396	$163.34	$163.35	$163.30
Purchase #4	$72.57	13.139%	$82.105	$82.11	$82.10	$82.10
Purchase #5	$126.26	11.870%	$141.2471	$141.25	$141.25	$141.20
Purchase #6	$40.63	4.447%	$42.4368	$42.44	$42.45	$42.40
Purchase #7	$104.95	4.128%	$109.2823	$109.28	$109.30	$109.30
7 purchase totals =	$533.28		$579.3800	$579.39	$579.40	$579.30