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	$233.93	3.235%	$241.4976	$241.50	$241.50	$241.50
Purchase #2	$25.89	7.700%	$27.8835	$27.88	$27.90	$27.90
Purchase #3	$44.89	10.507%	$49.6066	$49.61	$49.60	$49.60
Purchase #4	$14.54	9.317%	$15.8947	$15.89	$15.90	$15.90
Purchase #5	$133.50	11.147%	$148.3812	$148.38	$148.40	$148.40
Purchase #6	$179.40	5.146%	$188.6319	$188.63	$188.65	$188.60
Purchase #7	$95.73	13.810%	$108.9503	$108.95	$108.95	$109.00
7 purchase totals =	$727.88		$780.8458	$780.84	$780.90	$780.90