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	$35.35	13.489%	$40.1184	$40.12	$40.10	$40.10
Purchase #2	$47.89	7.571%	$51.5158	$51.52	$51.50	$51.50
Purchase #3	$236.82	6.411%	$252.0025	$252.00	$252.00	$252.00
Purchase #4	$135.35	12.627%	$152.4406	$152.44	$152.45	$152.40
Purchase #5	$176.45	5.593%	$186.3188	$186.32	$186.30	$186.30
Purchase #6	$131.87	7.527%	$141.7959	$141.80	$141.80	$141.80
Purchase #7	$138.27	10.127%	$152.2726	$152.27	$152.25	$152.30
7 purchase totals =	$902.00		$976.4646	$976.47	$976.40	$976.40