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	$112.71	13.384%	$127.7951	$127.80	$127.80	$127.80
Purchase #2	$90.52	5.180%	$95.2089	$95.21	$95.20	$95.20
Purchase #3	$110.44	12.406%	$124.1412	$124.14	$124.15	$124.10
Purchase #4	$101.35	4.114%	$105.5195	$105.52	$105.50	$105.50
Purchase #5	$154.84	5.662%	$163.607	$163.61	$163.60	$163.60
Purchase #6	$109.65	6.394%	$116.661	$116.66	$116.65	$116.70
Purchase #7	$33.36	13.773%	$37.9547	$37.95	$37.95	$38.00
7 purchase totals =	$712.87		$770.8874	$770.89	$770.85	$770.90