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	$36.72	11.252%	$40.8517	$40.85	$40.85	$40.90
Purchase #2	$82.89	7.630%	$89.2145	$89.21	$89.20	$89.20
Purchase #3	$89.66	12.134%	$100.5393	$100.54	$100.55	$100.50
Purchase #4	$53.46	4.239%	$55.7262	$55.73	$55.75	$55.70
Purchase #5	$18.35	10.341%	$20.2476	$20.25	$20.25	$20.20
Purchase #6	$12.75	11.845%	$14.2602	$14.26	$14.25	$14.30
Purchase #7	$153.43	11.858%	$171.6237	$171.62	$171.60	$171.60
7 purchase totals =	$447.26		$492.4632	$492.46	$492.45	$492.40