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	$69.80	12.483%	$78.5131	$78.51	$78.50	$78.50
Purchase #2	$241.42	8.667%	$262.3439	$262.34	$262.35	$262.30
Purchase #3	$115.29	11.637%	$128.7063	$128.71	$128.70	$128.70
Purchase #4	$24.62	13.184%	$27.8659	$27.87	$27.85	$27.90
Purchase #5	$223.43	9.391%	$244.4123	$244.41	$244.40	$244.40
Purchase #6	$127.82	11.236%	$142.1819	$142.18	$142.20	$142.20
Purchase #7	$71.32	7.771%	$76.8623	$76.86	$76.85	$76.90
7 purchase totals =	$873.70		$960.8857	$960.88	$960.85	$960.90