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	$124.57	9.486%	$136.3867	$136.39	$136.40	$136.40
Purchase #2	$26.48	9.244%	$28.9278	$28.93	$28.95	$28.90
Purchase #3	$65.86	9.318%	$71.9968	$72.00	$72.00	$72.00
Purchase #4	$15.34	13.631%	$17.431	$17.43	$17.45	$17.40
Purchase #5	$179.48	5.591%	$189.5147	$189.51	$189.50	$189.50
Purchase #6	$47.76	12.574%	$53.7653	$53.77	$53.75	$53.80
Purchase #7	$9.38	12.171%	$10.5216	$10.52	$10.50	$10.50
7 purchase totals =	$468.87		$508.5439	$508.55	$508.55	$508.50