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	$63.85	10.214%	$70.3716	$70.37	$70.35	$70.40
Purchase #2	$124.91	5.375%	$131.6239	$131.62	$131.60	$131.60
Purchase #3	$146.44	6.820%	$156.4272	$156.43	$156.45	$156.40
Purchase #4	$143.29	7.865%	$154.5598	$154.56	$154.55	$154.60
Purchase #5	$74.25	3.126%	$76.5711	$76.57	$76.55	$76.60
Purchase #6	$12.88	5.150%	$13.5433	$13.54	$13.55	$13.50
Purchase #7	$57.72	10.714%	$63.9041	$63.90	$63.90	$63.90
7 purchase totals =	$623.34		$667.0010	$666.99	$666.95	$667.00