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	$11.32	11.589%	$12.6319	$12.63	$12.65	$12.60
Purchase #2	$100.73	13.575%	$114.4041	$114.40	$114.40	$114.40
Purchase #3	$43.95	13.727%	$49.983	$49.98	$50.00	$50.00
Purchase #4	$29.53	6.830%	$31.5469	$31.55	$31.55	$31.50
Purchase #5	$43.86	3.779%	$45.5175	$45.52	$45.50	$45.50
Purchase #6	$215.49	10.586%	$238.3018	$238.30	$238.30	$238.30
Purchase #7	$92.47	5.357%	$97.4236	$97.42	$97.40	$97.40
7 purchase totals =	$537.35		$589.8088	$589.80	$589.80	$589.70