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	$80.57	9.666%	$88.3579	$88.36	$88.35	$88.40
Purchase #2	$133.32	13.165%	$150.8716	$150.87	$150.85	$150.90
Purchase #3	$214.83	12.575%	$241.8449	$241.84	$241.85	$241.80
Purchase #4	$133.49	12.692%	$150.4326	$150.43	$150.45	$150.40
Purchase #5	$250.90	12.667%	$282.6815	$282.68	$282.70	$282.70
Purchase #6	$91.93	9.248%	$100.4317	$100.43	$100.45	$100.40
Purchase #7	$142.78	9.623%	$156.5197	$156.52	$156.50	$156.50
7 purchase totals =	$1,047.82		$1,171.1399	$1,171.13	$1,171.15	$1,171.10