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	$115.71	6.404%	$123.1201	$123.12	$123.10	$123.10
Purchase #2	$69.57	3.403%	$71.9375	$71.94	$71.95	$71.90
Purchase #3	$233.46	6.496%	$248.6256	$248.63	$248.65	$248.60
Purchase #4	$241.67	3.210%	$249.4276	$249.43	$249.45	$249.40
Purchase #5	$186.67	5.164%	$196.3096	$196.31	$196.30	$196.30
Purchase #6	$107.29	6.494%	$114.2574	$114.26	$114.25	$114.30
Purchase #7	$68.71	11.478%	$76.5965	$76.60	$76.60	$76.60
7 purchase totals =	$1,023.08		$1,080.2743	$1,080.29	$1,080.30	$1,080.20