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	$48.85	5.466%	$51.5201	$51.52	$51.50	$51.50
Purchase #2	$52.46	3.552%	$54.3234	$54.32	$54.30	$54.30
Purchase #3	$166.54	13.341%	$188.7581	$188.76	$188.75	$188.80
Purchase #4	$53.78	10.578%	$59.4688	$59.47	$59.45	$59.50
Purchase #5	$104.80	9.760%	$115.0285	$115.03	$115.05	$115.00
Purchase #6	$51.28	11.190%	$57.0182	$57.02	$57.00	$57.00
Purchase #7	$247.73	5.313%	$260.8919	$260.89	$260.90	$260.90
7 purchase totals =	$725.44		$787.0090	$787.01	$786.95	$787.00