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	$185.96	10.460%	$205.4114	$205.41	$205.40	$205.40
Purchase #2	$120.91	5.301%	$127.3194	$127.32	$127.30	$127.30
Purchase #3	$169.58	10.214%	$186.9009	$186.90	$186.90	$186.90
Purchase #4	$144.52	4.182%	$150.5638	$150.56	$150.55	$150.60
Purchase #5	$101.89	3.247%	$105.1984	$105.20	$105.20	$105.20
Purchase #6	$37.71	5.171%	$39.66	$39.66	$39.65	$39.70
Purchase #7	$33.42	3.440%	$34.5696	$34.57	$34.55	$34.60
7 purchase totals =	$793.99		$849.6235	$849.62	$849.55	$849.70