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	$133.81	10.824%	$148.2936	$148.29	$148.30	$148.30
Purchase #2	$177.28	11.729%	$198.0732	$198.07	$198.05	$198.10
Purchase #3	$249.80	12.254%	$280.4105	$280.41	$280.40	$280.40
Purchase #4	$223.85	3.461%	$231.5974	$231.60	$231.60	$231.60
Purchase #5	$57.50	4.131%	$59.8753	$59.88	$59.90	$59.90
Purchase #6	$188.44	6.539%	$200.7621	$200.76	$200.75	$200.80
Purchase #7	$129.54	5.860%	$137.131	$137.13	$137.15	$137.10
7 purchase totals =	$1,160.22		$1,256.1431	$1,256.14	$1,256.15	$1,256.20