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	$110.47	12.570%	$124.3561	$124.36	$124.35	$124.40
Purchase #2	$130.37	8.351%	$141.2572	$141.26	$141.25	$141.30
Purchase #3	$57.90	8.554%	$62.8528	$62.85	$62.85	$62.90
Purchase #4	$138.83	5.787%	$146.8641	$146.86	$146.85	$146.90
Purchase #5	$25.69	10.488%	$28.3844	$28.38	$28.40	$28.40
Purchase #6	$131.61	11.874%	$147.2374	$147.24	$147.25	$147.20
Purchase #7	$103.98	9.776%	$114.1451	$114.15	$114.15	$114.10
7 purchase totals =	$698.85		$765.0971	$765.10	$765.10	$765.20