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	$57.29	6.556%	$61.0459	$61.05	$61.05	$61.00
Purchase #2	$41.48	9.662%	$45.4878	$45.49	$45.50	$45.50
Purchase #3	$216.37	9.194%	$236.2631	$236.26	$236.25	$236.30
Purchase #4	$123.98	12.627%	$139.635	$139.64	$139.65	$139.60
Purchase #5	$196.61	12.320%	$220.8324	$220.83	$220.85	$220.80
Purchase #6	$36.90	8.719%	$40.1173	$40.12	$40.10	$40.10
Purchase #7	$117.65	8.376%	$127.5044	$127.50	$127.50	$127.50
7 purchase totals =	$790.28		$870.8859	$870.89	$870.90	$870.80