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	$7.38	9.111%	$8.0524	$8.05	$8.05	$8.10
Purchase #2	$28.69	11.850%	$32.0898	$32.09	$32.10	$32.10
Purchase #3	$144.81	12.298%	$162.6187	$162.62	$162.60	$162.60
Purchase #4	$105.65	5.829%	$111.8083	$111.81	$111.80	$111.80
Purchase #5	$115.32	3.696%	$119.5822	$119.58	$119.60	$119.60
Purchase #6	$246.30	8.138%	$266.3439	$266.34	$266.35	$266.30
Purchase #7	$39.35	7.279%	$42.2143	$42.21	$42.20	$42.20
7 purchase totals =	$687.50		$742.7096	$742.70	$742.70	$742.70