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	$122.38	13.278%	$138.6296	$138.63	$138.65	$138.60
Purchase #2	$160.76	12.871%	$181.4514	$181.45	$181.45	$181.50
Purchase #3	$124.76	4.216%	$130.0199	$130.02	$130.00	$130.00
Purchase #4	$56.27	6.740%	$60.0626	$60.06	$60.05	$60.10
Purchase #5	$63.99	5.733%	$67.6585	$67.66	$67.65	$67.70
Purchase #6	$154.94	10.524%	$171.2459	$171.25	$171.25	$171.20
Purchase #7	$123.90	6.422%	$131.8569	$131.86	$131.85	$131.90
7 purchase totals =	$807.00		$880.9248	$880.93	$880.90	$881.00