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	$34.83	9.841%	$38.2576	$38.26	$38.25	$38.30
Purchase #2	$94.28	4.156%	$98.1983	$98.20	$98.20	$98.20
Purchase #3	$63.74	4.304%	$66.4834	$66.48	$66.50	$66.50
Purchase #4	$97.65	12.503%	$109.8592	$109.86	$109.85	$109.90
Purchase #5	$87.83	13.456%	$99.6484	$99.65	$99.65	$99.60
Purchase #6	$81.66	10.486%	$90.2229	$90.22	$90.20	$90.20
Purchase #7	$80.59	11.756%	$90.0642	$90.06	$90.05	$90.10
7 purchase totals =	$540.58		$592.7340	$592.73	$592.70	$592.80