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	$120.43	6.114%	$127.7931	$127.79	$127.80	$127.80
Purchase #2	$126.64	4.142%	$131.8854	$131.89	$131.90	$131.90
Purchase #3	$233.30	3.125%	$240.5906	$240.59	$240.60	$240.60
Purchase #4	$116.63	5.537%	$123.0878	$123.09	$123.10	$123.10
Purchase #5	$161.49	10.693%	$178.7581	$178.76	$178.75	$178.80
Purchase #6	$94.81	5.833%	$100.3403	$100.34	$100.35	$100.30
Purchase #7	$184.25	12.417%	$207.1283	$207.13	$207.15	$207.10
7 purchase totals =	$1,037.55		$1,109.5836	$1,109.59	$1,109.65	$1,109.60