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	$236.33	12.608%	$266.1265	$266.13	$266.15	$266.10
Purchase #2	$40.50	10.182%	$44.6237	$44.62	$44.60	$44.60
Purchase #3	$191.67	12.156%	$214.9694	$214.97	$214.95	$215.00
Purchase #4	$118.25	13.780%	$134.5449	$134.54	$134.55	$134.50
Purchase #5	$174.96	5.228%	$184.1069	$184.11	$184.10	$184.10
Purchase #6	$100.25	12.296%	$112.5767	$112.58	$112.60	$112.60
Purchase #7	$94.64	5.546%	$99.8887	$99.89	$99.90	$99.90
7 purchase totals =	$956.60		$1,056.8368	$1,056.84	$1,056.85	$1,056.80