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	$43.57	13.870%	$49.6132	$49.61	$49.60	$49.60
Purchase #2	$164.88	12.290%	$185.1438	$185.14	$185.15	$185.10
Purchase #3	$121.42	13.636%	$137.9768	$137.98	$138.00	$138.00
Purchase #4	$64.89	3.400%	$67.0963	$67.10	$67.10	$67.10
Purchase #5	$101.37	13.838%	$115.3976	$115.40	$115.40	$115.40
Purchase #6	$160.43	5.244%	$168.8429	$168.84	$168.85	$168.80
Purchase #7	$41.98	8.525%	$45.5588	$45.56	$45.55	$45.60
7 purchase totals =	$698.54		$769.6294	$769.63	$769.65	$769.60