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	$117.88	5.143%	$123.9426	$123.94	$123.95	$123.90
Purchase #2	$131.83	10.309%	$145.4204	$145.42	$145.40	$145.40
Purchase #3	$144.67	12.335%	$162.515	$162.52	$162.50	$162.50
Purchase #4	$148.38	12.440%	$166.8385	$166.84	$166.85	$166.80
Purchase #5	$110.95	12.565%	$124.8909	$124.89	$124.90	$124.90
Purchase #6	$23.60	3.366%	$24.3944	$24.39	$24.40	$24.40
Purchase #7	$167.77	12.725%	$189.1187	$189.12	$189.10	$189.10
7 purchase totals =	$845.08		$937.1205	$937.12	$937.10	$937.00