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	$88.95	12.804%	$100.3392	$100.34	$100.35	$100.30
Purchase #2	$222.97	8.707%	$242.384	$242.38	$242.40	$242.40
Purchase #3	$56.85	9.677%	$62.3514	$62.35	$62.35	$62.40
Purchase #4	$115.86	9.259%	$126.5875	$126.59	$126.60	$126.60
Purchase #5	$161.93	7.140%	$173.4918	$173.49	$173.50	$173.50
Purchase #6	$178.59	6.525%	$190.243	$190.24	$190.25	$190.20
Purchase #7	$114.47	12.285%	$128.5326	$128.53	$128.55	$128.50
7 purchase totals =	$939.62		$1,023.9295	$1,023.92	$1,024.00	$1,023.90