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	$156.69	6.508%	$166.8874	$166.89	$166.90	$166.90
Purchase #2	$95.40	10.749%	$105.6545	$105.65	$105.65	$105.70
Purchase #3	$127.87	3.771%	$132.692	$132.69	$132.70	$132.70
Purchase #4	$36.44	4.144%	$37.9501	$37.95	$37.95	$38.00
Purchase #5	$137.89	13.463%	$156.4541	$156.45	$156.45	$156.50
Purchase #6	$212.63	13.117%	$240.5207	$240.52	$240.50	$240.50
Purchase #7	$125.86	11.618%	$140.4824	$140.48	$140.50	$140.50
7 purchase totals =	$892.78		$980.6412	$980.63	$980.65	$980.80