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	$85.63	4.604%	$89.5724	$89.57	$89.55	$89.60
Purchase #2	$205.93	10.607%	$227.773	$227.77	$227.75	$227.80
Purchase #3	$150.90	3.738%	$156.5406	$156.54	$156.55	$156.50
Purchase #4	$138.52	5.197%	$145.7189	$145.72	$145.70	$145.70
Purchase #5	$182.34	9.720%	$200.0634	$200.06	$200.05	$200.10
Purchase #6	$241.29	6.221%	$256.3007	$256.30	$256.30	$256.30
Purchase #7	$90.92	11.711%	$101.5676	$101.57	$101.55	$101.60
7 purchase totals =	$1,095.53		$1,177.5366	$1,177.53	$1,177.45	$1,177.60