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	$131.38	11.602%	$146.6227	$146.62	$146.60	$146.60
Purchase #2	$156.98	7.368%	$168.5463	$168.55	$168.55	$168.50
Purchase #3	$126.79	3.661%	$131.4318	$131.43	$131.45	$131.40
Purchase #4	$10.88	8.470%	$11.8015	$11.80	$11.80	$11.80
Purchase #5	$144.56	11.410%	$161.0543	$161.05	$161.05	$161.10
Purchase #6	$37.59	3.124%	$38.7643	$38.76	$38.75	$38.80
Purchase #7	$113.43	12.827%	$127.9797	$127.98	$128.00	$128.00
7 purchase totals =	$721.61		$786.2006	$786.19	$786.20	$786.20