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	$54.67	9.606%	$59.9216	$59.92	$59.90	$59.90
Purchase #2	$86.29	4.321%	$90.0186	$90.02	$90.00	$90.00
Purchase #3	$69.66	5.592%	$73.5554	$73.56	$73.55	$73.60
Purchase #4	$25.47	12.257%	$28.5919	$28.59	$28.60	$28.60
Purchase #5	$214.91	11.257%	$239.1024	$239.10	$239.10	$239.10
Purchase #6	$239.81	4.730%	$251.153	$251.15	$251.15	$251.20
Purchase #7	$210.38	11.628%	$234.843	$234.84	$234.85	$234.80
7 purchase totals =	$901.19		$977.1859	$977.18	$977.15	$977.20