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	$249.31	12.527%	$280.5411	$280.54	$280.55	$280.50
Purchase #2	$92.98	8.447%	$100.834	$100.83	$100.85	$100.80
Purchase #3	$85.27	12.142%	$95.6235	$95.62	$95.60	$95.60
Purchase #4	$248.85	13.333%	$282.0292	$282.03	$282.05	$282.00
Purchase #5	$140.96	11.196%	$156.7419	$156.74	$156.75	$156.70
Purchase #6	$239.28	4.276%	$249.5116	$249.51	$249.50	$249.50
Purchase #7	$149.36	7.327%	$160.3036	$160.30	$160.30	$160.30
7 purchase totals =	$1,206.01		$1,325.5849	$1,325.57	$1,325.60	$1,325.40