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	$229.72	5.733%	$242.8898	$242.89	$242.90	$242.90
Purchase #2	$102.85	4.167%	$107.1358	$107.14	$107.15	$107.10
Purchase #3	$132.53	13.648%	$150.6177	$150.62	$150.60	$150.60
Purchase #4	$36.43	4.162%	$37.9462	$37.95	$37.95	$37.90
Purchase #5	$42.71	6.327%	$45.4123	$45.41	$45.40	$45.40
Purchase #6	$243.65	4.873%	$255.5231	$255.52	$255.50	$255.50
Purchase #7	$214.86	11.383%	$239.3175	$239.32	$239.30	$239.30
7 purchase totals =	$1,002.75		$1,078.8424	$1,078.85	$1,078.80	$1,078.70