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	$227.86	5.549%	$240.504	$240.50	$240.50	$240.50
Purchase #2	$99.92	10.688%	$110.5994	$110.60	$110.60	$110.60
Purchase #3	$136.32	6.175%	$144.7378	$144.74	$144.75	$144.70
Purchase #4	$162.80	4.600%	$170.2888	$170.29	$170.30	$170.30
Purchase #5	$140.92	6.451%	$150.0107	$150.01	$150.00	$150.00
Purchase #6	$105.90	3.490%	$109.5959	$109.60	$109.60	$109.60
Purchase #7	$156.78	3.448%	$162.1858	$162.19	$162.20	$162.20
7 purchase totals =	$1,030.50		$1,087.9224	$1,087.93	$1,087.95	$1,087.90