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	$55.28	3.812%	$57.3873	$57.39	$57.40	$57.40
Purchase #2	$72.83	10.626%	$80.5689	$80.57	$80.55	$80.60
Purchase #3	$160.74	7.123%	$172.1895	$172.19	$172.20	$172.20
Purchase #4	$49.41	12.136%	$55.4064	$55.41	$55.40	$55.40
Purchase #5	$124.37	7.355%	$133.5174	$133.52	$133.50	$133.50
Purchase #6	$190.51	5.195%	$200.407	$200.41	$200.40	$200.40
Purchase #7	$65.25	7.816%	$70.3499	$70.35	$70.35	$70.30
7 purchase totals =	$718.39		$769.8264	$769.84	$769.80	$769.80