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	$137.25	3.322%	$141.8094	$141.81	$141.80	$141.80
Purchase #2	$172.97	3.429%	$178.9011	$178.90	$178.90	$178.90
Purchase #3	$235.41	5.598%	$248.5883	$248.59	$248.60	$248.60
Purchase #4	$241.85	5.495%	$255.1397	$255.14	$255.15	$255.10
Purchase #5	$107.66	6.682%	$114.8538	$114.85	$114.85	$114.90
Purchase #6	$29.51	7.540%	$31.7351	$31.74	$31.75	$31.70
Purchase #7	$94.40	8.779%	$102.6874	$102.69	$102.70	$102.70
7 purchase totals =	$1,019.05		$1,073.7148	$1,073.72	$1,073.75	$1,073.70