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	$36.58	7.511%	$39.3275	$39.33	$39.35	$39.30
Purchase #2	$87.47	10.148%	$96.3465	$96.35	$96.35	$96.30
Purchase #3	$146.27	11.105%	$162.5133	$162.51	$162.50	$162.50
Purchase #4	$118.51	11.142%	$131.7144	$131.71	$131.70	$131.70
Purchase #5	$68.96	5.624%	$72.8383	$72.84	$72.85	$72.80
Purchase #6	$214.47	5.247%	$225.7232	$225.72	$225.70	$225.70
Purchase #7	$239.62	5.125%	$251.9005	$251.90	$251.90	$251.90
7 purchase totals =	$911.88		$980.3637	$980.36	$980.35	$980.20