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	$225.94	13.473%	$256.3809	$256.38	$256.40	$256.40
Purchase #2	$131.76	7.218%	$141.2704	$141.27	$141.25	$141.30
Purchase #3	$10.25	5.796%	$10.8441	$10.84	$10.85	$10.80
Purchase #4	$206.90	12.673%	$233.1204	$233.12	$233.10	$233.10
Purchase #5	$9.91	10.397%	$10.9403	$10.94	$10.95	$10.90
Purchase #6	$86.45	11.524%	$96.4125	$96.41	$96.40	$96.40
Purchase #7	$51.75	3.172%	$53.3915	$53.39	$53.40	$53.40
7 purchase totals =	$722.96		$802.3601	$802.35	$802.35	$802.30