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	$155.88	9.334%	$170.4298	$170.43	$170.45	$170.40
Purchase #2	$61.73	6.241%	$65.5826	$65.58	$65.60	$65.60
Purchase #3	$247.52	9.681%	$271.4824	$271.48	$271.50	$271.50
Purchase #4	$94.93	5.743%	$100.3818	$100.38	$100.40	$100.40
Purchase #5	$42.39	4.309%	$44.2166	$44.22	$44.20	$44.20
Purchase #6	$163.59	12.612%	$184.222	$184.22	$184.20	$184.20
Purchase #7	$22.37	11.789%	$25.0072	$25.01	$25.00	$25.00
7 purchase totals =	$788.41		$861.3224	$861.32	$861.35	$861.30