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	$120.98	13.760%	$137.6268	$137.63	$137.65	$137.60
Purchase #2	$41.85	4.290%	$43.6454	$43.65	$43.65	$43.60
Purchase #3	$56.89	4.706%	$59.5672	$59.57	$59.55	$59.60
Purchase #4	$241.71	8.575%	$262.4366	$262.44	$262.45	$262.40
Purchase #5	$191.26	5.550%	$201.8749	$201.87	$201.85	$201.90
Purchase #6	$129.99	12.199%	$145.8475	$145.85	$145.85	$145.80
Purchase #7	$69.72	13.153%	$78.8903	$78.89	$78.90	$78.90
7 purchase totals =	$852.40		$929.8887	$929.90	$929.90	$929.80