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	$109.65	6.647%	$116.9384	$116.94	$116.95	$116.90
Purchase #2	$86.90	6.665%	$92.6919	$92.69	$92.70	$92.70
Purchase #3	$20.94	13.793%	$23.8283	$23.83	$23.85	$23.80
Purchase #4	$171.95	9.700%	$188.6292	$188.63	$188.65	$188.60
Purchase #5	$28.74	7.287%	$30.8343	$30.83	$30.85	$30.80
Purchase #6	$80.38	11.297%	$89.4605	$89.46	$89.45	$89.50
Purchase #7	$132.61	8.287%	$143.5994	$143.60	$143.60	$143.60
7 purchase totals =	$631.17		$685.9820	$685.98	$686.05	$685.90