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	$76.62	4.650%	$80.1828	$80.18	$80.20	$80.20
Purchase #2	$56.27	5.405%	$59.3114	$59.31	$59.30	$59.30
Purchase #3	$59.39	6.807%	$63.4327	$63.43	$63.45	$63.40
Purchase #4	$228.62	4.442%	$238.7753	$238.78	$238.80	$238.80
Purchase #5	$20.67	9.737%	$22.6826	$22.68	$22.70	$22.70
Purchase #6	$234.60	11.826%	$262.3438	$262.34	$262.35	$262.30
Purchase #7	$122.39	7.441%	$131.497	$131.50	$131.50	$131.50
7 purchase totals =	$798.56		$858.2256	$858.22	$858.30	$858.20