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	$37.84	9.572%	$41.462	$41.46	$41.45	$41.50
Purchase #2	$216.25	10.296%	$238.5151	$238.52	$238.50	$238.50
Purchase #3	$65.91	12.688%	$74.2727	$74.27	$74.25	$74.30
Purchase #4	$96.46	6.259%	$102.4974	$102.50	$102.50	$102.50
Purchase #5	$45.26	3.243%	$46.7278	$46.73	$46.75	$46.70
Purchase #6	$135.70	10.566%	$150.0381	$150.04	$150.05	$150.00
Purchase #7	$81.99	9.607%	$89.8668	$89.87	$89.85	$89.90
7 purchase totals =	$679.41		$743.3799	$743.39	$743.35	$743.40