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	$220.84	10.278%	$243.5379	$243.54	$243.55	$243.50
Purchase #2	$43.67	11.232%	$48.575	$48.58	$48.60	$48.60
Purchase #3	$80.60	11.170%	$89.603	$89.60	$89.60	$89.60
Purchase #4	$136.94	11.281%	$152.3882	$152.39	$152.40	$152.40
Purchase #5	$132.37	8.734%	$143.9312	$143.93	$143.95	$143.90
Purchase #6	$22.73	10.167%	$25.041	$25.04	$25.05	$25.00
Purchase #7	$134.49	4.147%	$140.0673	$140.07	$140.05	$140.10
7 purchase totals =	$771.64		$843.1436	$843.15	$843.20	$843.10