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	$114.83	5.415%	$121.048	$121.05	$121.05	$121.00
Purchase #2	$82.52	9.235%	$90.1407	$90.14	$90.15	$90.10
Purchase #3	$59.78	11.725%	$66.7892	$66.79	$66.80	$66.80
Purchase #4	$201.89	7.396%	$216.8218	$216.82	$216.80	$216.80
Purchase #5	$90.74	6.768%	$96.8813	$96.88	$96.90	$96.90
Purchase #6	$142.35	7.545%	$153.0903	$153.09	$153.10	$153.10
Purchase #7	$103.92	10.588%	$114.923	$114.92	$114.90	$114.90
7 purchase totals =	$796.03		$859.6943	$859.69	$859.70	$859.60