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	$77.89	9.175%	$85.0364	$85.04	$85.05	$85.00
Purchase #2	$46.86	5.409%	$49.3947	$49.39	$49.40	$49.40
Purchase #3	$235.88	13.837%	$268.5187	$268.52	$268.50	$268.50
Purchase #4	$178.56	12.342%	$200.5979	$200.60	$200.60	$200.60
Purchase #5	$57.82	11.407%	$64.4155	$64.42	$64.40	$64.40
Purchase #6	$133.45	5.147%	$140.3187	$140.32	$140.30	$140.30
Purchase #7	$152.52	11.633%	$170.2627	$170.26	$170.25	$170.30
7 purchase totals =	$882.98		$978.5446	$978.55	$978.50	$978.50