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	$54.46	6.603%	$58.056	$58.06	$58.05	$58.10
Purchase #2	$131.37	5.593%	$138.7175	$138.72	$138.70	$138.70
Purchase #3	$228.59	4.266%	$238.3416	$238.34	$238.35	$238.30
Purchase #4	$222.65	4.858%	$233.4663	$233.47	$233.45	$233.50
Purchase #5	$97.51	11.629%	$108.8494	$108.85	$108.85	$108.80
Purchase #6	$193.51	6.188%	$205.4844	$205.48	$205.50	$205.50
Purchase #7	$10.63	3.644%	$11.0174	$11.02	$11.00	$11.00
7 purchase totals =	$938.72		$993.9326	$993.94	$993.90	$993.90