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	$124.50	7.135%	$133.3831	$133.38	$133.40	$133.40
Purchase #2	$116.98	7.291%	$125.509	$125.51	$125.50	$125.50
Purchase #3	$204.47	5.516%	$215.7486	$215.75	$215.75	$215.70
Purchase #4	$39.73	9.759%	$43.6073	$43.61	$43.60	$43.60
Purchase #5	$81.31	11.321%	$90.5151	$90.52	$90.50	$90.50
Purchase #6	$19.29	7.186%	$20.6762	$20.68	$20.70	$20.70
Purchase #7	$83.44	13.454%	$94.666	$94.67	$94.65	$94.70
7 purchase totals =	$669.72		$724.1053	$724.12	$724.10	$724.10