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	$35.75	9.859%	$39.2746	$39.27	$39.25	$39.30
Purchase #2	$56.39	5.805%	$59.6634	$59.66	$59.65	$59.70
Purchase #3	$41.31	8.299%	$44.7383	$44.74	$44.75	$44.70
Purchase #4	$27.76	4.718%	$29.0697	$29.07	$29.05	$29.10
Purchase #5	$169.80	9.227%	$185.4674	$185.47	$185.45	$185.50
Purchase #6	$247.25	6.155%	$262.4682	$262.47	$262.45	$262.50
Purchase #7	$164.97	13.412%	$187.0958	$187.10	$187.10	$187.10
7 purchase totals =	$743.23		$807.7774	$807.78	$807.70	$807.90