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	$107.97	10.794%	$119.6243	$119.62	$119.60	$119.60
Purchase #2	$18.74	8.836%	$20.3959	$20.40	$20.40	$20.40
Purchase #3	$238.81	7.431%	$256.556	$256.56	$256.55	$256.60
Purchase #4	$76.49	11.338%	$85.1624	$85.16	$85.15	$85.20
Purchase #5	$222.61	3.171%	$229.669	$229.67	$229.65	$229.70
Purchase #6	$59.59	11.734%	$66.5823	$66.58	$66.60	$66.60
Purchase #7	$45.78	12.114%	$51.3258	$51.33	$51.35	$51.30
7 purchase totals =	$769.99		$829.3157	$829.32	$829.30	$829.40