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	$149.97	9.676%	$164.4811	$164.48	$164.50	$164.50
Purchase #2	$136.87	11.752%	$152.955	$152.96	$152.95	$153.00
Purchase #3	$129.73	3.327%	$134.0461	$134.05	$134.05	$134.00
Purchase #4	$140.67	12.801%	$158.6772	$158.68	$158.70	$158.70
Purchase #5	$150.83	10.363%	$166.4605	$166.46	$166.45	$166.50
Purchase #6	$29.72	9.312%	$32.4875	$32.49	$32.50	$32.50
Purchase #7	$160.99	5.481%	$169.8139	$169.81	$169.80	$169.80
7 purchase totals =	$898.78		$978.9213	$978.93	$978.95	$979.00