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	$99.74	11.828%	$111.5372	$111.54	$111.55	$111.50
Purchase #2	$216.55	5.354%	$228.1441	$228.14	$228.15	$228.10
Purchase #3	$84.78	9.362%	$92.7171	$92.72	$92.70	$92.70
Purchase #4	$172.56	5.857%	$182.6668	$182.67	$182.65	$182.70
Purchase #5	$248.87	6.670%	$265.4696	$265.47	$265.45	$265.50
Purchase #6	$56.32	11.411%	$62.7467	$62.75	$62.75	$62.70
Purchase #7	$130.47	5.707%	$137.9159	$137.92	$137.90	$137.90
7 purchase totals =	$1,009.29		$1,081.1974	$1,081.21	$1,081.15	$1,081.10