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	$164.96	13.193%	$186.7232	$186.72	$186.70	$186.70
Purchase #2	$69.96	9.178%	$76.3809	$76.38	$76.40	$76.40
Purchase #3	$91.59	8.623%	$99.4878	$99.49	$99.50	$99.50
Purchase #4	$55.45	8.678%	$60.262	$60.26	$60.25	$60.30
Purchase #5	$115.85	10.597%	$128.1266	$128.13	$128.15	$128.10
Purchase #6	$89.60	11.415%	$99.8278	$99.83	$99.85	$99.80
Purchase #7	$202.36	12.382%	$227.4162	$227.42	$227.40	$227.40
7 purchase totals =	$789.77		$878.2245	$878.23	$878.25	$878.20