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	$163.37	9.864%	$179.4848	$179.48	$179.50	$179.50
Purchase #2	$99.79	13.820%	$113.581	$113.58	$113.60	$113.60
Purchase #3	$103.89	5.349%	$109.4471	$109.45	$109.45	$109.40
Purchase #4	$143.49	3.458%	$148.4519	$148.45	$148.45	$148.50
Purchase #5	$50.64	10.318%	$55.865	$55.87	$55.85	$55.90
Purchase #6	$175.68	11.850%	$196.4981	$196.50	$196.50	$196.50
Purchase #7	$163.54	7.164%	$175.256	$175.26	$175.25	$175.30
7 purchase totals =	$900.40		$978.5839	$978.59	$978.60	$978.70