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	$162.28	3.543%	$168.0296	$168.03	$168.05	$168.00
Purchase #2	$237.66	7.456%	$255.3799	$255.38	$255.40	$255.40
Purchase #3	$43.88	4.215%	$45.7295	$45.73	$45.75	$45.70
Purchase #4	$31.84	6.320%	$33.8523	$33.85	$33.85	$33.90
Purchase #5	$123.85	10.365%	$136.6871	$136.69	$136.70	$136.70
Purchase #6	$156.76	3.874%	$162.8329	$162.83	$162.85	$162.80
Purchase #7	$152.93	3.515%	$158.3055	$158.31	$158.30	$158.30
7 purchase totals =	$909.20		$960.8168	$960.82	$960.90	$960.80