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	$57.42	4.586%	$60.0533	$60.05	$60.05	$60.10
Purchase #2	$117.40	11.649%	$131.0759	$131.08	$131.10	$131.10
Purchase #3	$188.51	5.864%	$199.5642	$199.56	$199.55	$199.60
Purchase #4	$81.45	5.498%	$85.9281	$85.93	$85.95	$85.90
Purchase #5	$65.32	9.522%	$71.5398	$71.54	$71.55	$71.50
Purchase #6	$129.30	7.368%	$138.8268	$138.83	$138.85	$138.80
Purchase #7	$154.46	12.284%	$173.4339	$173.43	$173.45	$173.40
7 purchase totals =	$793.86		$860.4220	$860.42	$860.50	$860.40