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	$99.85	13.557%	$113.3867	$113.39	$113.40	$113.40
Purchase #2	$98.47	3.309%	$101.7284	$101.73	$101.75	$101.70
Purchase #3	$35.65	6.506%	$37.9694	$37.97	$37.95	$38.00
Purchase #4	$10.81	12.752%	$12.1885	$12.19	$12.20	$12.20
Purchase #5	$100.83	8.328%	$109.2271	$109.23	$109.25	$109.20
Purchase #6	$157.47	13.773%	$179.1583	$179.16	$179.15	$179.20
Purchase #7	$215.88	8.469%	$234.1629	$234.16	$234.15	$234.20
7 purchase totals =	$718.96		$787.8213	$787.83	$787.85	$787.90