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	$158.72	3.409%	$164.1308	$164.13	$164.15	$164.10
Purchase #2	$48.30	9.829%	$53.0474	$53.05	$53.05	$53.00
Purchase #3	$218.94	12.383%	$246.0513	$246.05	$246.05	$246.10
Purchase #4	$86.34	3.574%	$89.4258	$89.43	$89.45	$89.40
Purchase #5	$9.68	5.283%	$10.1914	$10.19	$10.20	$10.20
Purchase #6	$94.96	4.482%	$99.2161	$99.22	$99.20	$99.20
Purchase #7	$153.83	10.244%	$169.5883	$169.59	$169.60	$169.60
7 purchase totals =	$770.77		$831.6511	$831.66	$831.70	$831.60