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	$216.70	6.855%	$231.5548	$231.55	$231.55	$231.60
Purchase #2	$111.72	11.254%	$124.293	$124.29	$124.30	$124.30
Purchase #3	$119.65	3.580%	$123.9335	$123.93	$123.95	$123.90
Purchase #4	$226.48	11.138%	$251.7053	$251.71	$251.70	$251.70
Purchase #5	$43.89	3.601%	$45.4705	$45.47	$45.45	$45.50
Purchase #6	$42.27	5.192%	$44.4647	$44.46	$44.45	$44.50
Purchase #7	$146.77	4.579%	$153.4906	$153.49	$153.50	$153.50
7 purchase totals =	$907.48		$974.9124	$974.90	$974.90	$975.00