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	$144.78	12.493%	$162.8674	$162.87	$162.85	$162.90
Purchase #2	$151.38	11.516%	$168.8129	$168.81	$168.80	$168.80
Purchase #3	$229.80	5.511%	$242.4643	$242.46	$242.45	$242.50
Purchase #4	$93.47	6.611%	$99.6493	$99.65	$99.65	$99.60
Purchase #5	$5.25	12.635%	$5.9133	$5.91	$5.90	$5.90
Purchase #6	$231.87	10.634%	$256.5271	$256.53	$256.55	$256.50
Purchase #7	$45.46	13.240%	$51.4789	$51.48	$51.50	$51.50
7 purchase totals =	$902.01		$987.7132	$987.71	$987.70	$987.70