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	$151.82	13.379%	$172.132	$172.13	$172.15	$172.10
Purchase #2	$121.42	13.226%	$137.479	$137.48	$137.50	$137.50
Purchase #3	$171.64	8.248%	$185.7969	$185.80	$185.80	$185.80
Purchase #4	$169.66	11.117%	$188.5211	$188.52	$188.50	$188.50
Purchase #5	$20.52	7.733%	$22.1068	$22.11	$22.10	$22.10
Purchase #6	$236.72	7.868%	$255.3451	$255.35	$255.35	$255.30
Purchase #7	$249.59	12.264%	$280.1997	$280.20	$280.20	$280.20
7 purchase totals =	$1,121.37		$1,241.5806	$1,241.59	$1,241.60	$1,241.50