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	$96.55	3.832%	$100.2498	$100.25	$100.25	$100.20
Purchase #2	$103.96	11.533%	$115.9497	$115.95	$115.95	$115.90
Purchase #3	$242.93	12.528%	$273.3643	$273.36	$273.35	$273.40
Purchase #4	$95.50	5.468%	$100.7219	$100.72	$100.70	$100.70
Purchase #5	$54.50	9.184%	$59.5053	$59.51	$59.50	$59.50
Purchase #6	$128.38	4.176%	$133.7411	$133.74	$133.75	$133.70
Purchase #7	$74.88	13.763%	$85.1857	$85.19	$85.20	$85.20
7 purchase totals =	$796.70		$868.7178	$868.72	$868.70	$868.60