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	$32.26	5.397%	$34.0011	$34.00	$34.00	$34.00
Purchase #2	$148.45	12.765%	$167.3996	$167.40	$167.40	$167.40
Purchase #3	$16.80	9.324%	$18.3664	$18.37	$18.35	$18.40
Purchase #4	$6.94	7.494%	$7.4601	$7.46	$7.45	$7.50
Purchase #5	$85.88	4.867%	$90.0598	$90.06	$90.05	$90.10
Purchase #6	$181.72	10.419%	$200.6534	$200.65	$200.65	$200.70
Purchase #7	$139.52	10.273%	$153.8529	$153.85	$153.85	$153.90
7 purchase totals =	$611.57		$671.7933	$671.79	$671.75	$672.00