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	$116.40	4.575%	$121.7253	$121.73	$121.75	$121.70
Purchase #2	$192.29	10.822%	$213.0996	$213.10	$213.10	$213.10
Purchase #3	$202.96	9.597%	$222.4381	$222.44	$222.45	$222.40
Purchase #4	$196.67	10.190%	$216.7107	$216.71	$216.70	$216.70
Purchase #5	$46.59	10.740%	$51.5938	$51.59	$51.60	$51.60
Purchase #6	$40.33	5.492%	$42.5449	$42.54	$42.55	$42.50
Purchase #7	$113.98	8.327%	$123.4711	$123.47	$123.45	$123.50
7 purchase totals =	$909.22		$991.5835	$991.58	$991.60	$991.50