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	$27.80	4.610%	$29.0816	$29.08	$29.10	$29.10
Purchase #2	$123.88	6.376%	$131.7786	$131.78	$131.80	$131.80
Purchase #3	$160.30	8.567%	$174.0329	$174.03	$174.05	$174.00
Purchase #4	$38.37	11.828%	$42.9084	$42.91	$42.90	$42.90
Purchase #5	$218.45	9.482%	$239.1634	$239.16	$239.15	$239.20
Purchase #6	$33.51	3.287%	$34.6115	$34.61	$34.60	$34.60
Purchase #7	$12.38	8.795%	$13.4688	$13.47	$13.45	$13.50
7 purchase totals =	$614.69		$665.0452	$665.04	$665.05	$665.10