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	$128.53	8.607%	$139.5926	$139.59	$139.60	$139.60
Purchase #2	$174.56	3.212%	$180.1669	$180.17	$180.15	$180.20
Purchase #3	$125.90	8.847%	$137.0384	$137.04	$137.05	$137.00
Purchase #4	$44.92	3.249%	$46.3795	$46.38	$46.40	$46.40
Purchase #5	$188.54	11.789%	$210.767	$210.77	$210.75	$210.80
Purchase #6	$20.51	5.152%	$21.5667	$21.57	$21.55	$21.60
Purchase #7	$87.52	3.365%	$90.465	$90.47	$90.45	$90.50
7 purchase totals =	$770.48		$825.9761	$825.99	$825.95	$826.10