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	$26.34	4.769%	$27.5962	$27.60	$27.60	$27.60
Purchase #2	$84.55	6.685%	$90.2022	$90.20	$90.20	$90.20
Purchase #3	$164.25	3.490%	$169.9823	$169.98	$170.00	$170.00
Purchase #4	$242.34	4.617%	$253.5288	$253.53	$253.55	$253.50
Purchase #5	$176.33	8.291%	$190.9495	$190.95	$190.95	$190.90
Purchase #6	$82.54	5.195%	$86.828	$86.83	$86.85	$86.80
Purchase #7	$81.78	9.304%	$89.3888	$89.39	$89.40	$89.40
7 purchase totals =	$858.13		$908.4758	$908.48	$908.55	$908.40