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	$129.46	6.468%	$137.8335	$137.83	$137.85	$137.80
Purchase #2	$34.34	7.246%	$36.8283	$36.83	$36.85	$36.80
Purchase #3	$6.53	9.811%	$7.1707	$7.17	$7.15	$7.20
Purchase #4	$103.68	4.141%	$107.9734	$107.97	$107.95	$108.00
Purchase #5	$41.47	4.455%	$43.3175	$43.32	$43.30	$43.30
Purchase #6	$114.71	10.398%	$126.6375	$126.64	$126.65	$126.60
Purchase #7	$134.67	5.333%	$141.852	$141.85	$141.85	$141.90
7 purchase totals =	$564.86		$601.6129	$601.61	$601.60	$601.60