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	$52.55	12.315%	$59.0215	$59.02	$59.00	$59.00
Purchase #2	$23.82	11.869%	$26.6472	$26.65	$26.65	$26.60
Purchase #3	$50.80	9.569%	$55.6611	$55.66	$55.65	$55.70
Purchase #4	$233.46	4.716%	$244.47	$244.47	$244.45	$244.50
Purchase #5	$53.93	5.225%	$56.7478	$56.75	$56.75	$56.70
Purchase #6	$118.65	12.820%	$133.8609	$133.86	$133.85	$133.90
Purchase #7	$86.75	5.115%	$91.1873	$91.19	$91.20	$91.20
7 purchase totals =	$619.96		$667.5958	$667.60	$667.55	$667.60