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	$194.29	10.246%	$214.197	$214.20	$214.20	$214.20
Purchase #2	$11.87	5.627%	$12.5379	$12.54	$12.55	$12.50
Purchase #3	$73.97	5.680%	$78.1715	$78.17	$78.15	$78.20
Purchase #4	$57.53	6.621%	$61.3391	$61.34	$61.35	$61.30
Purchase #5	$72.73	9.208%	$79.427	$79.43	$79.45	$79.40
Purchase #6	$17.64	10.562%	$19.5031	$19.50	$19.50	$19.50
Purchase #7	$84.29	6.291%	$89.5927	$89.59	$89.60	$89.60
7 purchase totals =	$512.32		$554.7683	$554.77	$554.80	$554.70