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	$49.33	4.818%	$51.7067	$51.71	$51.70	$51.70
Purchase #2	$45.88	5.554%	$48.4282	$48.43	$48.45	$48.40
Purchase #3	$86.28	11.111%	$95.8666	$95.87	$95.85	$95.90
Purchase #4	$97.87	12.759%	$110.3572	$110.36	$110.35	$110.40
Purchase #5	$52.86	3.168%	$54.5346	$54.53	$54.55	$54.50
Purchase #6	$169.60	5.315%	$178.6142	$178.61	$178.60	$178.60
Purchase #7	$27.74	12.758%	$31.2791	$31.28	$31.30	$31.30
7 purchase totals =	$529.56		$570.7866	$570.79	$570.80	$570.80