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	$235.43	6.487%	$250.7023	$250.70	$250.70	$250.70
Purchase #2	$217.85	7.742%	$234.7159	$234.72	$234.70	$234.70
Purchase #3	$94.31	6.513%	$100.4524	$100.45	$100.45	$100.50
Purchase #4	$113.37	4.583%	$118.5657	$118.57	$118.55	$118.60
Purchase #5	$38.65	5.596%	$40.8129	$40.81	$40.80	$40.80
Purchase #6	$147.63	13.723%	$167.8893	$167.89	$167.90	$167.90
Purchase #7	$58.34	3.818%	$60.5674	$60.57	$60.55	$60.60
7 purchase totals =	$905.58		$973.7059	$973.71	$973.65	$973.80