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	$80.36	11.632%	$89.7075	$89.71	$89.70	$89.70
Purchase #2	$235.33	13.208%	$266.4124	$266.41	$266.40	$266.40
Purchase #3	$235.46	7.692%	$253.5716	$253.57	$253.55	$253.60
Purchase #4	$108.60	4.269%	$113.2361	$113.24	$113.25	$113.20
Purchase #5	$130.88	8.562%	$142.0859	$142.09	$142.10	$142.10
Purchase #6	$86.38	5.341%	$90.9936	$90.99	$91.00	$91.00
Purchase #7	$92.46	9.654%	$101.3861	$101.39	$101.40	$101.40
7 purchase totals =	$969.47		$1,057.3932	$1,057.40	$1,057.40	$1,057.40