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	$88.98	5.119%	$93.5349	$93.53	$93.55	$93.50
Purchase #2	$94.65	8.670%	$102.8562	$102.86	$102.85	$102.90
Purchase #3	$132.54	4.223%	$138.1372	$138.14	$138.15	$138.10
Purchase #4	$127.29	4.296%	$132.7584	$132.76	$132.75	$132.80
Purchase #5	$153.71	12.208%	$172.4749	$172.47	$172.45	$172.50
Purchase #6	$78.50	6.642%	$83.714	$83.71	$83.70	$83.70
Purchase #7	$154.51	6.438%	$164.4574	$164.46	$164.45	$164.50
7 purchase totals =	$830.18		$887.9330	$887.93	$887.90	$888.00