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	$49.90	6.244%	$53.0158	$53.02	$53.00	$53.00
Purchase #2	$11.56	13.255%	$13.0923	$13.09	$13.10	$13.10
Purchase #3	$139.30	5.645%	$147.1635	$147.16	$147.15	$147.20
Purchase #4	$29.39	8.706%	$31.9487	$31.95	$31.95	$31.90
Purchase #5	$69.52	11.489%	$77.5072	$77.51	$77.50	$77.50
Purchase #6	$176.63	11.317%	$196.6192	$196.62	$196.60	$196.60
Purchase #7	$51.71	9.666%	$56.7083	$56.71	$56.70	$56.70
7 purchase totals =	$528.01		$576.0550	$576.06	$576.00	$576.00