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	$73.88	4.591%	$77.2718	$77.27	$77.25	$77.30
Purchase #2	$168.74	6.314%	$179.3942	$179.39	$179.40	$179.40
Purchase #3	$52.27	12.761%	$58.9402	$58.94	$58.95	$58.90
Purchase #4	$131.44	9.451%	$143.8624	$143.86	$143.85	$143.90
Purchase #5	$89.32	10.601%	$98.7888	$98.79	$98.80	$98.80
Purchase #6	$134.76	5.848%	$142.6408	$142.64	$142.65	$142.60
Purchase #7	$85.60	8.494%	$92.8709	$92.87	$92.85	$92.90
7 purchase totals =	$736.01		$793.7691	$793.76	$793.75	$793.80