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	$79.40	12.710%	$89.4917	$89.49	$89.50	$89.50
Purchase #2	$84.37	5.532%	$89.0373	$89.04	$89.05	$89.00
Purchase #3	$63.35	4.569%	$66.2445	$66.24	$66.25	$66.20
Purchase #4	$123.72	4.716%	$129.5546	$129.55	$129.55	$129.60
Purchase #5	$24.86	5.222%	$26.1582	$26.16	$26.15	$26.20
Purchase #6	$29.71	9.688%	$32.5883	$32.59	$32.60	$32.60
Purchase #7	$150.48	13.563%	$170.8896	$170.89	$170.90	$170.90
7 purchase totals =	$555.89		$603.9642	$603.96	$604.00	$604.00