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	$230.89	7.609%	$248.4584	$248.46	$248.45	$248.50
Purchase #2	$99.82	9.715%	$109.5175	$109.52	$109.50	$109.50
Purchase #3	$105.28	10.803%	$116.6534	$116.65	$116.65	$116.70
Purchase #4	$208.83	8.863%	$227.3386	$227.34	$227.35	$227.30
Purchase #5	$122.41	7.738%	$131.8821	$131.88	$131.90	$131.90
Purchase #6	$36.87	10.463%	$40.7277	$40.73	$40.75	$40.70
Purchase #7	$206.35	4.129%	$214.8702	$214.87	$214.85	$214.90
7 purchase totals =	$1,010.45		$1,089.4479	$1,089.45	$1,089.45	$1,089.50