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	$36.53	8.840%	$39.7593	$39.76	$39.75	$39.80
Purchase #2	$33.62	11.594%	$37.5179	$37.52	$37.50	$37.50
Purchase #3	$183.50	9.340%	$200.6389	$200.64	$200.65	$200.60
Purchase #4	$249.64	12.401%	$280.5979	$280.60	$280.60	$280.60
Purchase #5	$81.74	6.157%	$86.7727	$86.77	$86.75	$86.80
Purchase #6	$249.87	12.438%	$280.9488	$280.95	$280.95	$280.90
Purchase #7	$250.44	11.594%	$279.476	$279.48	$279.50	$279.50
7 purchase totals =	$1,085.34		$1,205.7115	$1,205.72	$1,205.70	$1,205.70