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	$248.27	4.610%	$259.7152	$259.72	$259.70	$259.70
Purchase #2	$138.48	10.131%	$152.5094	$152.51	$152.50	$152.50
Purchase #3	$33.88	12.419%	$38.0876	$38.09	$38.10	$38.10
Purchase #4	$52.52	5.179%	$55.24	$55.24	$55.25	$55.20
Purchase #5	$116.84	5.257%	$122.9823	$122.98	$123.00	$123.00
Purchase #6	$38.89	10.526%	$42.9836	$42.98	$43.00	$43.00
Purchase #7	$24.62	5.213%	$25.9034	$25.90	$25.90	$25.90
7 purchase totals =	$653.50		$697.4215	$697.42	$697.45	$697.40