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	$60.67	3.113%	$62.5587	$62.56	$62.55	$62.60
Purchase #2	$168.86	12.834%	$190.5315	$190.53	$190.55	$190.50
Purchase #3	$204.61	10.426%	$225.9426	$225.94	$225.95	$225.90
Purchase #4	$104.97	3.385%	$108.5232	$108.52	$108.50	$108.50
Purchase #5	$81.93	6.281%	$87.076	$87.08	$87.10	$87.10
Purchase #6	$40.76	7.403%	$43.7775	$43.78	$43.80	$43.80
Purchase #7	$153.74	7.386%	$165.0952	$165.10	$165.10	$165.10
7 purchase totals =	$815.54		$883.5047	$883.51	$883.55	$883.50