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	$235.96	8.309%	$255.5659	$255.57	$255.55	$255.60
Purchase #2	$135.71	13.135%	$153.5355	$153.54	$153.55	$153.50
Purchase #3	$108.27	4.169%	$112.7838	$112.78	$112.80	$112.80
Purchase #4	$204.86	6.316%	$217.799	$217.80	$217.80	$217.80
Purchase #5	$41.95	12.253%	$47.0901	$47.09	$47.10	$47.10
Purchase #6	$132.63	13.300%	$150.2698	$150.27	$150.25	$150.30
Purchase #7	$55.56	7.111%	$59.5109	$59.51	$59.50	$59.50
7 purchase totals =	$914.94		$996.5550	$996.56	$996.55	$996.60