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	$227.97	12.656%	$256.8219	$256.82	$256.80	$256.80
Purchase #2	$237.82	10.237%	$262.1656	$262.17	$262.15	$262.20
Purchase #3	$191.77	10.850%	$212.577	$212.58	$212.60	$212.60
Purchase #4	$18.67	4.322%	$19.4769	$19.48	$19.50	$19.50
Purchase #5	$24.72	3.237%	$25.5202	$25.52	$25.50	$25.50
Purchase #6	$203.76	12.329%	$228.8816	$228.88	$228.90	$228.90
Purchase #7	$56.79	12.751%	$64.0313	$64.03	$64.05	$64.00
7 purchase totals =	$961.50		$1,069.4745	$1,069.48	$1,069.50	$1,069.50