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	$77.48	3.867%	$80.4762	$80.48	$80.50	$80.50
Purchase #2	$76.97	6.547%	$82.0092	$82.01	$82.00	$82.00
Purchase #3	$196.49	9.119%	$214.4079	$214.41	$214.40	$214.40
Purchase #4	$46.88	8.364%	$50.801	$50.80	$50.80	$50.80
Purchase #5	$108.45	5.625%	$114.5503	$114.55	$114.55	$114.60
Purchase #6	$179.73	5.841%	$190.228	$190.23	$190.25	$190.20
Purchase #7	$145.79	4.316%	$152.0823	$152.08	$152.10	$152.10
7 purchase totals =	$831.79		$884.5549	$884.56	$884.60	$884.60