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	$131.86	8.822%	$143.4927	$143.49	$143.50	$143.50
Purchase #2	$75.70	7.193%	$81.1451	$81.15	$81.15	$81.10
Purchase #3	$175.50	10.442%	$193.8257	$193.83	$193.85	$193.80
Purchase #4	$50.53	8.874%	$55.014	$55.01	$55.00	$55.00
Purchase #5	$50.89	9.113%	$55.5276	$55.53	$55.55	$55.50
Purchase #6	$53.54	4.484%	$55.9407	$55.94	$55.95	$55.90
Purchase #7	$74.52	10.324%	$82.2134	$82.21	$82.20	$82.20
7 purchase totals =	$612.54		$667.1592	$667.16	$667.20	$667.00