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	$20.94	12.170%	$23.4884	$23.49	$23.50	$23.50
Purchase #2	$85.28	3.542%	$88.3006	$88.30	$88.30	$88.30
Purchase #3	$153.76	9.582%	$168.4933	$168.49	$168.50	$168.50
Purchase #4	$34.87	4.481%	$36.4325	$36.43	$36.45	$36.40
Purchase #5	$141.66	6.170%	$150.4004	$150.40	$150.40	$150.40
Purchase #6	$44.83	12.644%	$50.4983	$50.50	$50.50	$50.50
Purchase #7	$96.42	3.637%	$99.9268	$99.93	$99.95	$99.90
7 purchase totals =	$577.76		$617.5403	$617.54	$617.60	$617.50