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	$13.87	12.761%	$15.64	$15.64	$15.65	$15.60
Purchase #2	$92.68	5.127%	$97.4317	$97.43	$97.45	$97.40
Purchase #3	$99.38	4.443%	$103.7955	$103.80	$103.80	$103.80
Purchase #4	$14.34	3.237%	$14.8042	$14.80	$14.80	$14.80
Purchase #5	$81.26	11.732%	$90.7934	$90.79	$90.80	$90.80
Purchase #6	$88.68	4.415%	$92.5952	$92.60	$92.60	$92.60
Purchase #7	$59.67	4.826%	$62.5497	$62.55	$62.55	$62.50
7 purchase totals =	$449.88		$477.6097	$477.61	$477.65	$477.50