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	$54.42	3.849%	$56.5146	$56.51	$56.50	$56.50
Purchase #2	$37.87	5.269%	$39.8654	$39.87	$39.85	$39.90
Purchase #3	$120.31	6.803%	$128.4947	$128.49	$128.50	$128.50
Purchase #4	$146.50	5.843%	$155.06	$155.06	$155.05	$155.10
Purchase #5	$81.45	13.117%	$92.1338	$92.13	$92.15	$92.10
Purchase #6	$13.86	7.870%	$14.9508	$14.95	$14.95	$15.00
Purchase #7	$89.89	13.440%	$101.9712	$101.97	$101.95	$102.00
7 purchase totals =	$544.30		$588.9905	$588.98	$588.95	$589.10