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	$103.32	5.675%	$109.1834	$109.18	$109.20	$109.20
Purchase #2	$233.75	10.575%	$258.4691	$258.47	$258.45	$258.50
Purchase #3	$119.31	7.689%	$128.4837	$128.48	$128.50	$128.50
Purchase #4	$196.52	4.835%	$206.0217	$206.02	$206.00	$206.00
Purchase #5	$109.89	12.321%	$123.4295	$123.43	$123.45	$123.40
Purchase #6	$132.37	3.284%	$136.717	$136.72	$136.70	$136.70
Purchase #7	$10.46	10.402%	$11.548	$11.55	$11.55	$11.50
7 purchase totals =	$905.62		$973.8524	$973.85	$973.85	$973.80