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	$182.92	12.377%	$205.56	$205.56	$205.55	$205.60
Purchase #2	$141.78	6.544%	$151.0581	$151.06	$151.05	$151.10
Purchase #3	$250.45	5.641%	$264.5779	$264.58	$264.60	$264.60
Purchase #4	$49.83	10.253%	$54.9391	$54.94	$54.95	$54.90
Purchase #5	$154.85	8.520%	$168.0432	$168.04	$168.05	$168.00
Purchase #6	$46.57	4.814%	$48.8119	$48.81	$48.80	$48.80
Purchase #7	$223.80	5.830%	$236.8475	$236.85	$236.85	$236.80
7 purchase totals =	$1,050.20		$1,129.8377	$1,129.84	$1,129.85	$1,129.80