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	$138.54	4.174%	$144.3227	$144.32	$144.30	$144.30
Purchase #2	$174.40	7.348%	$187.2149	$187.21	$187.20	$187.20
Purchase #3	$199.46	6.790%	$213.0033	$213.00	$213.00	$213.00
Purchase #4	$5.26	6.362%	$5.5946	$5.59	$5.60	$5.60
Purchase #5	$59.36	4.162%	$61.8306	$61.83	$61.85	$61.80
Purchase #6	$112.71	13.276%	$127.6734	$127.67	$127.65	$127.70
Purchase #7	$159.64	8.270%	$172.8422	$172.84	$172.85	$172.80
7 purchase totals =	$849.37		$912.4817	$912.46	$912.45	$912.40