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	$12.87	9.491%	$14.0915	$14.09	$14.10	$14.10
Purchase #2	$39.59	7.582%	$42.5917	$42.59	$42.60	$42.60
Purchase #3	$137.98	12.499%	$155.2261	$155.23	$155.25	$155.20
Purchase #4	$37.40	5.518%	$39.4637	$39.46	$39.45	$39.50
Purchase #5	$228.27	3.107%	$235.3623	$235.36	$235.35	$235.40
Purchase #6	$165.62	3.741%	$171.8158	$171.82	$171.80	$171.80
Purchase #7	$246.69	13.819%	$280.7801	$280.78	$280.80	$280.80
7 purchase totals =	$868.42		$939.3312	$939.33	$939.35	$939.40