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	$246.51	13.848%	$280.6467	$280.65	$280.65	$280.60
Purchase #2	$71.88	9.728%	$78.8725	$78.87	$78.85	$78.90
Purchase #3	$102.42	4.281%	$106.8046	$106.80	$106.80	$106.80
Purchase #4	$114.25	3.414%	$118.1505	$118.15	$118.15	$118.20
Purchase #5	$58.89	3.617%	$61.0201	$61.02	$61.00	$61.00
Purchase #6	$106.88	7.491%	$114.8864	$114.89	$114.90	$114.90
Purchase #7	$133.44	13.827%	$151.8907	$151.89	$151.90	$151.90
7 purchase totals =	$834.27		$912.2715	$912.27	$912.25	$912.30