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	$55.41	9.298%	$60.562	$60.56	$60.55	$60.60
Purchase #2	$131.31	4.745%	$137.5407	$137.54	$137.55	$137.50
Purchase #3	$185.51	12.376%	$208.4687	$208.47	$208.45	$208.50
Purchase #4	$112.76	3.368%	$116.5578	$116.56	$116.55	$116.60
Purchase #5	$178.61	6.849%	$190.843	$190.84	$190.85	$190.80
Purchase #6	$64.93	6.766%	$69.3232	$69.32	$69.30	$69.30
Purchase #7	$126.72	7.534%	$136.2671	$136.27	$136.25	$136.30
7 purchase totals =	$855.25		$919.5625	$919.56	$919.50	$919.60