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	$85.91	4.399%	$89.6892	$89.69	$89.70	$89.70
Purchase #2	$90.37	9.810%	$99.2353	$99.24	$99.25	$99.20
Purchase #3	$133.26	10.125%	$146.7526	$146.75	$146.75	$146.80
Purchase #4	$213.60	9.822%	$234.5798	$234.58	$234.60	$234.60
Purchase #5	$31.48	3.863%	$32.6961	$32.70	$32.70	$32.70
Purchase #6	$80.46	3.433%	$83.2222	$83.22	$83.20	$83.20
Purchase #7	$158.69	12.207%	$178.0613	$178.06	$178.05	$178.10
7 purchase totals =	$793.77		$864.2365	$864.24	$864.25	$864.30